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The figure shows two concentric circles. If the length of chord AB is 80 units and chord AB is tangent to the smaller circle, what is the area of the shaded region? Express your answer in terms of $\pi$. [asy] defaultpen(linewidth(.8pt)); dotfactor=4; filldraw(circle((0,0),50),gray); filldraw(circle((0,0),30),white); ...
Call the point of tangency between the two circles $P$ and the center $O$. [asy] defaultpen(linewidth(.8pt)); dotfactor=4; filldraw(circle((0,0),50),gray); filldraw(circle((0,0),30),white); draw((-40,30)--(40,30)); draw((0,30)--(0,0)--(-40,30)); label("$P$",(0,30),N); label("$O$",(0,0),S); label("$A$",(-40,30),W); l...
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In the diagram below, points $A$, $B$, $C$, and $P$ are situated so that $PA=2$, $PB=3$, $PC=4$, and $BC=5$. What is the maximum possible area of $\triangle ABC$? [asy] defaultpen(linewidth(0.8)); size(150); pair B = (0,0), C = (5,0), A = (2,3), P = (2.2,2); draw(A--B--C--cycle^^B--P^^C--P^^A--P); label("$A$",A,N); lab...
We first observe that by the Pythagorean theorem $\triangle PBC$ must be a right triangle with right angle at $P$, since $PB=3$, $PC=4$, and $BC=5$. $[\triangle PBC]=\frac{1}{2}(3)(4) = 6=\frac{1}{2}(PH)(5)$. Hence, the altitude $\overline{PH}$ from $P$ to $\overline{BC}$ has length $\frac{12}{5}$. Let $h$ be the leng...
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What is the total volume in cubic feet of three boxes if each box is a cube with edge length 4 feet?
Each box has volume $4^3=64$ cubic feet. Thus, three boxes have volume $64\cdot3=\boxed{192}$ cubic feet.
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What is the sum of the number of faces, edges and vertices of a triangular prism? [asy] draw((0,0)--(10,0)--(5,8.7)--cycle); draw((0,0)--(20,20),dashed); draw((10,0)--(30,20)); draw((5,8.7)--(25,28.7)); draw((25,28.7)--(30,20)--(20,20)--cycle,dashed); draw((25,28.7)--(30,20)); [/asy]
Faces: There are $3$ on the sides, a top face, and a bottom face, so $5$. Edges: There are $3$ on the top, $3$ on the bottom, and $3$ connecting them, for $9$. Vertices: There are $3$ on the top and $3$ on the bottom, for $6$. So $5+9+6=\boxed{20}$.
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[asy] draw(circle((4,1),1),black+linewidth(.75)); draw((0,0)--(8,0)--(8,6)--cycle,black+linewidth(.75)); MP("A",(0,0),SW);MP("B",(8,0),SE);MP("C",(8,6),NE);MP("P",(4,1),NW); MP("8",(4,0),S);MP("6",(8,3),E);MP("10",(4,3),NW); MP("->",(5,1),E); dot((4,1)); [/asy]The sides of $\triangle ABC$ have lengths $6,8,$ and $10$. ...
[asy] draw(circle((4,1),1),black+linewidth(.75)); draw((0,0)--(8,0)--(8,6)--cycle,black+linewidth(.75)); draw((3,1)--(7,1)--(7,4)--cycle,black+linewidth(.75)); draw((3,1)--(3,0),black+linewidth(.75)); draw((3,1)--(2.4,1.8),black+linewidth(.75)); draw((7,1)--(8,1),black+linewidth(.75)); draw((7,1)--(7,0),black+linewidth...
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Triangle $ABC$ is an isosceles triangle with $AB=BC$. Point $D$ is the midpoint of both $\overline{BC}$ and $\overline{AE}$, and $\overline{CE}$ is 11 units long. What is the length of $\overline{BD}$? Express your answer as a decimal to the nearest tenth. [asy] draw((0,0)--(3,112^.5)--(6,0)--cycle); draw((6,0)--(9,1...
Because triangles $D$ is the midpoint of $\overline{BC}$ and $\overline{AE}$, $ABEC$ must be a parallelogram, so $AB=CE=11$. Then because triangle $ABC$ is isosceles, $BC=AB=11$. That means $BD= \frac{11}{2}$ or $\boxed{5.5}$.
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In $\triangle XYZ$, we have $\angle X = 90^\circ$ and $\tan Z = 7$. If $YZ = 100$, then what is $XY$?
[asy] pair X,Y,Z; X = (0,0); Y = (14,0); Z = (0,2); draw(X--Y--Z--X); draw(rightanglemark(Y,X,Z,23)); label("$X$",X,SW); label("$Y$",Y,SE); label("$Z$",Z,N); label("$100$",(Y+Z)/2,NE); label("$k$",(Z)/2,W); label("$7k$",Y/2,S); [/asy] Since $\triangle XYZ$ is a right triangle with $\angle X = 90^\circ$, w...
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What is the area, in square units, of the interior region formed by the lines $y = 2x - 4, y = -3x +16$ and the $y$-axis?
To find the vertices of the triangle, we find where the two lines $y=2x-4$ and $y=-3x+16$ intersect. Solving $2x-4=-3x+16$, we get $x=4$. Substituting $x=4$ back into $y=2x-4$, we find $y=4$. Therefore, $(4,4)$ is one of the vertices of the triangle. The other two vertices are the $y$-intercepts of the two lines, na...
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Medians are drawn from point $A$ and point $B$ in this right triangle to divide segments $\overline{BC}$ and $\overline{AC}$ in half, respectively. The lengths of the medians are 6 and $2\sqrt{11}$ units, respectively. How many units are in the length of segment $\overline{AB}$? [asy] draw((0,0)--(7,0)--(0,4)--(0,0)--...
We draw the medians as shown below. [asy] draw((0,0)--(7,0)--(0,4)--(0,0)--cycle,linewidth(2)); draw((0,1/2)--(1/2,1/2)--(1/2,0),linewidth(1)); draw((0,4)--(3.5,0)); draw((0,2)--(7,0)); label("$A$",(0,4),NW); label("$B$",(7,0),E); label("$C$",(0,0),SW); label("$M$",(3.5,0),S); label("$N$",(0,2),W); [/asy] From right ...
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The figure drawn is not to scale. Which of the five segments shown is the longest? [asy] pair A = (-3,0), B=(0,2), C=(3,0), D=(0,-1); draw(D(MP("A", A, W))--D(MP("B", B, N))--D(MP("C", C, E))--D(MP("D", D, S))--A); draw(B--D); MP("55^\circ", (0,-0.75), NW); MP("55^\circ", (0,-0.75), NE); MP("40^\circ", (0,1.5), SW); MP...
Looking at triangle $ABD$, we see that $\angle BAD = 180^\circ - \angle ABD - \angle ADB = 180^\circ - 40^\circ - 55^\circ = 85^\circ$. Then $\angle ABD < \angle ADB < \angle BAD$, so $AD < AB < BD$. Looking at triangle $BCD$, we see that $\angle BCD = 180^\circ - \angle CBD - \angle BDC = 180^\circ - 75^\circ - 55^\...
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A circle centered at $O$ is circumscribed about $\triangle ABC$ as follows: [asy] pair pA, pB, pC, pO; pO = (0, 0); pA = pO + dir(-20); pB = pO + dir(90); pC = pO + dir(190); draw(pA--pB--pC--pA); draw(pO--pA); draw(pO--pB); draw(pO--pC); label("$O$", pO, S); label("$110^\circ$", pO, NE); label("$100^\circ$", pO, NW); ...
We can see that $\angle AOC = 360^\circ - (110^\circ + 100^\circ) = 150^\circ.$ Now, $\triangle AOC$ and $\triangle AOB$ are both isosceles triangles. That means that $\angle OAC = \frac{1}{2} \cdot (180^\circ - 150^\circ) = 15^\circ$ and $\angle OAB = \frac{1}{2} \cdot (180^\circ - 110^\circ) = 35^\circ.$ Therefore, ...
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Rectangle $ABCD$ is the base of pyramid $PABCD$. If $AB = 8$, $BC = 4$, $\overline{PA}\perp \overline{AB}$, $\overline{PA}\perp\overline{AD}$, and $PA = 6$, then what is the volume of $PABCD$?
[asy] import three; triple A = (4,8,0); triple B= (4,0,0); triple C = (0,0,0); triple D = (0,8,0); triple P = (4,8,6); draw(B--P--D--A--B); draw(A--P); draw(C--P, dashed); draw(B--C--D,dashed); label("$A$",A,S); label("$B$",B,W); label("$C$",C,S); label("$D$",D,E); label("$P$",P,N); [/asy] Since $\overline{PA}$ is per...
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The shaded region shown consists of 11 unit squares and rests along the $x$-axis and the $y$-axis. The shaded region is rotated about the $x$-axis to form a solid. In cubic units, what is the volume of the resulting solid? Express your answer in simplest form in terms of $\pi$. [asy] defaultpen(linewidth(0.7)); fill((...
The resulting solid is the union of two cylinders: one whose radius is 5 units and whose height is 1 unit (the squares shown in light gray produce this cylinder), and the other whose radius is 2 units and whose height is 3 units (shown in dark gray). The sum of these volumes is $\pi(5)^2(1)+\pi(2)^2(3)=\boxed{37\pi}$ ...
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In a circle with center $O$, $AD$ is a diameter, $ABC$ is a chord, $BO = 5$, and $\angle ABO = \text{arc } CD = 60^\circ$. Find the length of $BC$. [asy] import graph; unitsize(2 cm); pair O, A, B, C, D; O = (0,0); A = dir(30); C = dir(160); B = (2*C + A)/3; D = -A; draw(Circle(O,1)); draw(C--A--D); draw(B--O); ...
Since arc $CD$ is $60^\circ$, $\angle CAD = 60^\circ/2 = 30^\circ$. Since triangle $AOC$ is isosceles with $AO = CO$, $\angle OCA = \angle OAC = 30^\circ$. [asy] import graph; unitsize(2 cm); pair O, A, B, C, D; O = (0,0); A = dir(30); C = dir(160); B = (2*C + A)/3; D = -A; draw(Circle(O,1)); draw(C--A--D); draw(B...
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A right circular cone sits on a table, pointing up. The cross-section triangle, perpendicular to the base, has a vertex angle of 60 degrees. The diameter of the cone's base is $12\sqrt{3}$ inches. A sphere is placed inside the cone so that it is tangent to the sides of the cone and sits on the table. What is the volume...
Since the vertex angle of the cross-section triangle measures $60^\circ$, the cross-section triangle is equilateral. Also, the cross-section of the sphere inscribed in the cone is a circle tangent to each of the triangle's sides. Call the vertices of the equilateral triangle $A$, $B$, and $C$, and let $O$ be the cent...
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A regular polygon has exterior angles each measuring 15 degrees. How many sides does the polygon have?
The measure of each exterior angle in a regular $n$-gon is $360/n$ degrees. Setting this expression equal to 15, we find $n=\boxed{24}$.
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A right cylindrical oil tank is $15$ feet tall and its circular bases have diameters of $4$ feet each. When the tank is lying flat on its side (not on one of the circular ends), the oil inside is $3$ feet deep. How deep, in feet, would the oil have been if the tank had been standing upright on one of its bases? Express...
Since the oil is $3$ feet deep, we want to find the ratio of the area of the part of the circle covered with oil (part under the horizontal line of the figure below) to the entire area of the circle. [asy] draw(Circle((0,0),2)); draw((-1.732,1)--(1.732,1)); draw((0,0)--(-1.732,1)); draw((0,0)--(1.732,1)); draw((0,0)--(...
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Eric builds a small pyramid for a school project. His pyramid has a height of twelve inches and a square base that measures ten inches on each side. Eric wants to find the smallest cube-shaped box to put his pyramid in so that he can safely bring it to school right side up. What is the volume of this box, in inches cub...
The height of the pyramid is $12$ inches, so the height of the box must be at least $12$ inches. The base of the pyramid is $10$ inches on each side, so the minimum dimensions of the length and width of the box must be $10$. Since we want a cube-shaped box, we need to choose the dimensions of the box so that everything...
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Regions I, II and III are bounded by squares. The perimeter of region I is 12 units and the perimeter of region II is 24 units. What is the ratio of the area of region I to the area of region III? Express your answer as a common fraction. [asy] draw((0,0)--(9,0)--(9,9)--(0,9)--(0,0)--cycle,linewidth(2)); draw((9,0)--(...
A side of square I has length 3, while a side of square II has length 6 (all sides have equal length). Therefore, a side of square III has length 9. Since the side length of square I is $\frac{1}{3}$ that of square III, and the ratio of their areas is the square of the ratio of their side lengths, the ratio of the ar...
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Let $C_1$ and $C_2$ be circles defined by $$ (x-10)^2+y^2=36 $$and $$ (x+15)^2+y^2=81, $$respectively. What is the length of the shortest line segment $\overline{PQ}$ that is tangent to $C_1$ at $P$ and to $C_2$ at $Q$?
The centers are at $A=(10,0)$ and $B=(-15,0)$, and the radii are 6 and 9, respectively. Since the internal tangent is shorter than the external tangent, $\overline{PQ}$ intersects $\overline{AB}$ at a point $D$ that divides $\overline{AB}$ into parts proportional to the radii. The right triangles $\triangle APD$ and ...
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In the diagram below, we have $AB = 24$ and $\angle ADB =90^\circ$. If $\sin A = \frac23$ and $\sin C = \frac13$, then what is $DC$? [asy] pair A,B,C,D; A = (0,0); B = (8*sqrt(5),16); D = (8*sqrt(5),0); C = (8*sqrt(5) + 32*sqrt(2),0); draw(D--B--A--C--B); label("$A$",A,SW); label("$B$",B,N); label("$C$",C,SE); label...
From right triangle $ABD$, we have $\sin A = \frac{BD}{AB} = \frac{BD}{24}$. Since $\sin A = \frac23$, we have $\frac23 = \frac{BD}{24}$, so $BD = \frac23\cdot 24 = 16$. From right triangle $BCD$, we have $\sin C = \frac{BD}{BC}=\frac{16}{BC}$. Since $\sin C = \frac13$, we have $\frac{16}{BC} = \frac13$. Therefore,...
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In triangle $ABC$, $AB = 11$, $AC = 13$, and $BC = 20$. The medians $AD$, $BE$, and $CF$ of triangle $ABC$ intersect at the centroid $G$. Let $P$ be the foot of the altitude from $G$ to $BC$. Find $GP$. [asy] unitsize(0.3 cm); pair A, B, C, D, E, F, G, P; A = (44/5,33/5); B = (0,0); C = (20,0); D = (B + C)/2; E =...
Let $Q$ be the foot of the altitude from $A$ to $BC$. Then triangles $AQD$ and $GPD$ are similar. Furthermore, \[\frac{GP}{AQ} = \frac{GD}{AD} = \frac{1}{3},\]so to find $GP$, we can find $AQ$. [asy] unitsize(0.3 cm); pair A, B, C, D, E, F, G, P, Q; A = (44/5,33/5); B = (0,0); C = (20,0); D = (B + C)/2; E = (C + A...
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Points $A$, $B$, $C$, and $T$ are in space such that each of $\overline{TA}$, $\overline{TB}$, and $\overline{TC}$ is perpendicular to the other two. If $TA = TB = 10$ and $TC = 9$, then what is the volume of pyramid $TABC$?
[asy] import three; triple A = (4,8,0); triple B= (4,0,0); triple C = (0,0,0); triple D = (0,8,0); triple P = (4,8,6); draw(B--P--D--A--B); draw(A--P); draw(B--D,dashed); label("$T$",A,S); label("$B$",B,W); label("$C$",D,E); label("$A$",P,N); [/asy] We can think of $TAB$ as the base of the pyramid, and $\overline{CT}$...
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A circle has a radius of three inches. The distance from the center of the circle to chord $CD$ is two inches. How many inches long is chord $CD$? Express your answer in simplest radical form.
Call the center of the circle O, and call the point where the radius of the circle bisects the chord E. Thus, the line segment from the center of the circle to point E has length 2, and we have $\triangle ODE$ with a leg of 2 and a hypotenuse of 3. Thus, the other leg, DE has length $\sqrt{5}$, and since DE is $\frac...
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Let $EFGH$, $EFDC$, and $EHBC$ be three adjacent square faces of a cube, for which $EC = 8$, and let $A$ be the eighth vertex of the cube. Let $I$, $J$, and $K$, be the points on $\overline{EF}$, $\overline{EH}$, and $\overline{EC}$, respectively, so that $EI = EJ = EK = 2$. A solid $S$ is obtained by drilling a tunnel...
[asy] import three; currentprojection = perspective(5,-40,12); defaultpen(linewidth(0.7)); pen l = linewidth(0.5) + linetype("10 2"); triple S=(1,0,0), T=(2,0,2), U=(8,6,8), V=(8,8,6), W=(2,2,0), X=(6,8,8); draw((1,0,0)--(8,0,0)--(8,0,8)--(0,0,8)--(0,0,1)); draw((1,0,0)--(8,0,0)--(8,8,0)--(0,8,0)--(0,1,0),l); draw((0,...
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In the configuration below, $\theta$ is measured in radians, $C$ is the center of the circle, $BCD$ and $ACE$ are line segments and $AB$ is tangent to the circle at $A$. [asy] defaultpen(fontsize(10pt)+linewidth(.8pt)); pair A=(0,-1), E=(0,1), C=(0,0), D=dir(10), F=dir(190), B=(-1/sin(10*pi/180))*dir(10); fill(Arc((0,0...
Well, the shaded sector's area is basically $\text{(ratio of } \theta \text{ to total angle of circle)} \times \text{(total area)} = \frac{\theta}{2\pi} \cdot (\pi r^2) = \frac{\theta}{2} \cdot (AC)^2$. In addition, if you let $\angle{ACB} = \theta$, then\[\tan \theta = \frac{AB}{AC}\]\[AB = AC\tan \theta = r\tan \thet...
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In triangle $BCD$, $\angle C = 90^\circ$, $CD = 3$, and $BD = \sqrt{13}$. What is $\tan B$?
[asy] pair B,C,D; B = (0,0); C = (2,0); D = (2,-3); draw(B--C--D--B); draw(rightanglemark(B,C,D,7)); label("$D$",D,SE); label("$B$",B,NW); label("$C$",C,NE); label("$3$",(C+D)/2,E); label("$\sqrt{13}$",(B+D)/2,SW); [/asy] Because $\triangle BCD$ is a right triangle, we know that $\tan B = \frac{CD}{BC}$. By the Pytha...
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Two sides of an isosceles triangle are 10 inches and 20 inches. If the shortest side of a similar triangle is 50 inches, what is the perimeter of the larger triangle?
First of all, the third side of the smaller triangle cannot be 10 inches because sides of 10, 10 and 20 inches would not form a triangle. The smaller triangle must have sides of 10, 20 and 20 inches. If the shortest side of the similar triangle is 50 inches, then the other two sides are 100 inches and 100 inches. Thus,...
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Square $ABCD$ has side length $1$ unit. Points $E$ and $F$ are on sides $AB$ and $CB$, respectively, with $AE = CF$. When the square is folded along the lines $DE$ and $DF$, sides $AD$ and $CD$ coincide and lie on diagonal $BD$. The length of segment $AE$ can be expressed in the form $\sqrt{k}-m$ units. What is the ...
We start by drawing a diagram. When the paper is folded, sides $AD$ and $CD$ coincide on the longer dashed line, and points $A$ and $C$ meet at $G$, as you can see below. [asy] draw((0,0)--(1,0)--(1,1)--(0,1)--cycle); draw((0,0)--(1,.4)); draw((0,0)--(.4,1)); draw((1,.4)--(.4,1),dashed); draw((0,0)--(.7,.7),dashed); ...
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Compute $\sin 45^\circ$.
Let $P$ be the point on the unit circle that is $45^\circ$ counterclockwise from $(1,0)$, and let $D$ be the foot of the altitude from $P$ to the $x$-axis, as shown below. [asy] pair A,C,P,O,D; draw((0,-1.2)--(0,1.2),p=black+1.2bp,Arrows(0.15cm)); draw((-1.2,0)--(1.2,0),p=black+1.2bp,Arrows(0.15cm)); A = (1,0); O...
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How many integer side lengths are possible to complete a triangle in which the other sides measure 6 units and 3 units?
By the Triangle Inequality, the unknown side must measure less than $6+3=9$ units. Also, the length of that side plus 3 units must be more than 6 units, so the unknown length must be more than 3 units. There are $\boxed{5}$ possible integer side lengths greater than 3 units and less than 9 units.
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Kadin makes a snowman by stacking snowballs of radius 2 inches, 3 inches, and 5 inches. Assuming all his snowballs are spherical, what is the total volume of snow he uses, in cubic inches? Express your answer in terms of $\pi$.
A sphere with radius $r$ has volume $\frac{4}{3}\pi r^3$. Thus, the snowballs with radius 2, 3, and 5 inches have volumes $\frac{4}{3}\pi(2^3)$, $\frac{4}{3}\pi(3^3)$, and $\frac{4}{3}\pi(5^3)$ cubic inches respectively. The total volume of snow used is thus \begin{align*} \frac{4}{3}\pi(2^3)+\frac{4}{3}\pi(3^3)+\fr...
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Increasing the radius of a cylinder by $6$ units increased the volume by $y$ cubic units. Increasing the height of the cylinder by $6$ units also increases the volume by $y$ cubic units. If the original height is $2$, then the original radius is: $\text{(A) } 2 \qquad \text{(B) } 4 \qquad \text{(C) } 6 \qquad \text{(D)...
We know that the volume of a cylinder is equal to $\pi r^2h$, where $r$ and $h$ are the radius and height, respectively. So we know that $2\pi (r+6)^2-2\pi r^2=y=\pi r^2(2+6)-2\pi r^2$. Expanding and rearranging, we get that $2\pi (12r+36)=6\pi r^2$. Divide both sides by $6\pi$ to get that $4r+12=r^2$, and rearrange to...
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Jimmy owns a cube-shaped container that measures $10$ inches on each side. He fills this container with water until it is half full. Then he throws ten giant ice cubes that measure $2$ inches on each side into the container. In inches cubed, how much of the container is unoccupied by ice or water?
First let's compute the volume of the container. The container measures $10\times10\times10$ so its volume is $$10\cdot10\cdot10=10^3=1000$$inches cubed. Since the container is only half full, there are $$\frac{1}{2}\cdot10^3=500$$inches cubed of water in it. Additionally, there are ten ice cubes each with a volume of...
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Quadrilateral $ABCD$ has right angles at $B$ and $C$, $\triangle ABC \sim \triangle BCD$, and $AB > BC$. There is a point $E$ in the interior of $ABCD$ such that $\triangle ABC \sim \triangle CEB$ and the area of $\triangle AED$ is $17$ times the area of $\triangle CEB$. What is $\tfrac{AB}{BC}$? $\textbf{(A) } 1+\sqrt...
Let $CD=1$, $BC=x$, and $AB=x^2$. Note that $AB/BC=x$. By the Pythagorean Theorem, $BD=\sqrt{x^2+1}$. Since $\triangle BCD \sim \triangle ABC \sim \triangle CEB$, the ratios of side lengths must be equal. Since $BC=x$, $CE=\frac{x^2}{\sqrt{x^2+1}}$ and $BE=\frac{x}{\sqrt{x^2+1}}$. Let F be a point on $\overline{BC}$ su...
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In the diagram, $\angle PQR=\angle PRQ$. If $QR=5$ and $PR=7$, what is the perimeter of $\triangle PQR$? [asy] draw((0,0)--(2.5,7.43)--(5,0)--cycle); label("5",(2.5,0),S); label("$Q$",(0,0),SW); label("$R$",(5,0),SE); label("$P$",(2.5,7.43),N); label("7",(4.2,3.7)); [/asy]
Since $\angle PQR=\angle PRQ$, then $\triangle PQR$ is an isosceles triangle and $PQ=PR=7$. Therefore, the perimeter of $\triangle PQR$ is $PQ+QR+PR=7+5+7=\boxed{19}$.
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Given $DC = 7$, $CB = 8$, $AB = \frac{1}{4}AD$, and $ED = \frac{4}{5}AD$, find $FC$. Express your answer as a decimal. [asy] draw((0,0)--(-20,0)--(-20,16)--cycle); draw((-13,0)--(-13,10.4)); draw((-5,0)--(-5,4)); draw((-5,0.5)--(-5+0.5,0.5)--(-5+0.5,0)); draw((-13,0.5)--(-13+0.5,0.5)--(-13+0.5,0)); draw((-20,0.5)--(-...
We can easily see that $\triangle ABG \sim \triangle ACF \sim \triangle ADE.$ First of all, $BD = AD - AB.$ Since $AB = \dfrac{1}{4}AD,$ we have that $BD = \dfrac{3}{4}AD.$ Since $BD$ is also $DC + CB = 15,$ we see that $AD = 20$ and $AB = 5.$ Now, we can easily find $ED = \dfrac{4}{5}AD = 16.$ Now, we see that $CA =...
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A circle is inscribed in a square, then a square is inscribed in this circle, and finally, a circle is inscribed in this square. What is the ratio of the area of the smaller circle to the area of the larger square?
Let the radius of the smaller circle be $r$. Then the side length of the smaller square is $2r$. The radius of the larger circle is half the length of the diagonal of the smaller square, so it is $\sqrt{2}r$. Hence the larger square has sides of length $2\sqrt{2}r$. The ratio of the area of the smaller circle to the ar...
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Compute $\sin 315^\circ$.
Let $P$ be the point on the unit circle that is $315^\circ$ counterclockwise from $(1,0)$, and let $D$ be the foot of the altitude from $P$ to the $x$-axis, as shown below. [asy] pair A,C,P,O,D; draw((0,-1.2)--(0,1.2),p=black+1.2bp,Arrows(0.15cm)); draw((-1.2,0)--(1.2,0),p=black+1.2bp,Arrows(0.15cm)); A = (1,0); ...
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A frustum of a right circular cone is formed by cutting a small cone off of the top of a larger cone. If a particular frustum has a lower base radius of 6 inches, an upper base radius of 3 inches, and a height of 4 inches, what is its lateral surface area? (The lateral surface area of a cone or frustum is the curved s...
We start by drawing the frustum. Let the top and bottom circles have centers $O_1$ and $O_2$ respectively, and label points $A$ and $B$ on the circumferences as shown such that $O_1$, $O_2$, $A$, and $B$ lie in the same plane. [asy] unitsize(0.5 cm); import geometry; defaultpen(linewidth(.8)+fontsize(10)); label("$O...
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An acute isosceles triangle, $ABC$, is inscribed in a circle. Through $B$ and $C$, tangents to the circle are drawn, meeting at point $D$. If $\angle ABC = \angle ACB = 2 \angle D$ and $\angle BAC = k \pi$ in radians, then find $k$. [asy] import graph; unitsize(2 cm); pair O, A, B, C, D; O = (0,0); A = dir(90); B...
Let $x = \angle BAC$. Angles $\angle BAC$, $\angle BCD$, and $\angle CBD$ all intercept the same circular arc, minor arc $BC$ with measure $2 \angle BAC = 2x$. Then $\angle BCD = \angle CBD = x$, so $\angle D = \pi - 2x$. Since $\angle ABC = \angle ACB$, $\angle ABC = (\pi - x)/2$. Then from the equation $\angle AB...
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Six boys stood equally spaced on a circle of radius 40 feet. Each boy walked to all of the other non-adjacent persons on the circle, shook their hands and then returned to his original spot on the circle before the next boy started his trip to shake hands with all of the other non-adjacent boys on the circle. After all...
The thicker solid line in the diagram shows the shortest path that one person could travel. The circle is equally divided into six 60-degree arcs, so the short distance is 40 feet, the same as a radius. The dotted line is a diameter that separates the quadrilateral into two 30-60-90 triangles. The longer leg is $(80\sq...
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In $\triangle XYZ$, we have $\angle X = 90^\circ$ and $\tan Z = 3$. What is $\cos Z$?
[asy] pair X,Y,Z; X = (0,0); Y = (15,0); Z = (0,5); draw(X--Y--Z--X); draw(rightanglemark(Y,X,Z,23)); label("$X$",X,SW); label("$Y$",Y,SE); label("$Z$",Z,N); //label("$100$",(Y+Z)/2,NE); label("$k$",(Z)/2,W); label("$3k$",Y/2,S); [/asy] Since $\triangle XYZ$ is a right triangle with $\angle X = 90^\circ$, we have $\ta...
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The angles of quadrilateral $ABCD$ satisfy $\angle A = 2\angle B = 3\angle C = 4\angle D$. What is the degree measure of $\angle A$, rounded to the nearest whole number?
Let $x$ be the degree measure of $\angle A$. Then the degree measures of angles $B$, $C$, and $D$ are $x/2$, $x/3$, and $x/4$, respectively. The degree measures of the four angles have a sum of 360, so \[ 360 = x+\frac{x}{2}+\frac{x}{3}+\frac{x}{4} = \frac{25x}{12}. \]Thus $x=(12\cdot 360)/25 = 172.8\approx \boxed{1...
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In the diagram, $\triangle XYZ$ is right-angled at $X,$ with $YX=60$ and $XZ=80.$ The point $W$ is on $YZ$ so that $WX$ is perpendicular to $YZ.$ Determine the length of $WZ.$ [asy] pair X, Y, Z, W; Y=(0,0); X=(36,48); Z=(100,0); W=(36,0); draw(X--Y--Z--X--W); label("Y", Y, SW); label("X", X, N); label("W", W, S); labe...
By the Pythagorean Theorem, \begin{align*} YZ^2 &= YX^2 + XZ^2 \\ &= 60^2+80^2 \\ &= 3600+6400 \\ &=10000, \end{align*} so $YZ=100.$ (We could also have found $YZ$ without using the Pythagorean Theorem by noticing that $\triangle XYZ$ is a right-angled triangle with its right-angle at $X$ and $XY=60=3\cdot 20$ and $XZ...
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A regular hexagon is inscribed in a circle and another regular hexagon is circumscribed about the same circle. What is the ratio of the area of the larger hexagon to the area of the smaller hexagon? Express your answer as a common fraction.
Form a triangle whose first vertex is the center of the circle and whose other two vertices are the midpoint and one of the endpoints of a side of the larger hexagon, as shown in the diagram. Since each interior angle of a regular hexagon is 120 degrees, this triangle is a 30-60-90 right triangle. Let $r$ be the radi...
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On square $ABCD$, point $E$ lies on side $AD$ and point $F$ lies on side $BC$, so that $BE=EF=FD=30$. Find the area of the square $ABCD$.
Drawing the square and examining the given lengths,[asy] size(2inch, 2inch); currentpen = fontsize(8pt); pair A = (0, 0); dot(A); label("$A$", A, plain.SW); pair B = (3, 0); dot(B); label("$B$", B, plain.SE); pair C = (3, 3); dot(C); label("$C$", C, plain.NE); pair D = (0, 3); dot(D); label("$D$", D, plain.NW); pair E ...
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In triangle $ABC$, $AB = 7$, $AC = 15$, and the length of median $AM$ is 10. Find the area of triangle $ABC$.
Extend $AM$ to $D$ so that $MD = MA$. Then triangles $AMB$ and $DMC$ are congruent, so triangles $ABC$ and $ACD$ have equal area. [asy] unitsize(0.3 cm); pair A, B, C, D, M; A = (-7/sqrt(37),42/sqrt(37)); B = (0,0); C = (2*sqrt(37),0); M = (B + C)/2; D = 2*M - A; draw(A--B--C--cycle); draw(A--D--C); label("$A$", ...
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In $\triangle PQR$, we have $PQ = QR = 34$ and $PR = 32$. Point $M$ is the midpoint of $\overline{QR}$. Find $PM$.
We start with a diagram, including median $\overline{QN}$, which is also an altitude. Let the medians intersect at $G$, the centroid of the triangle. [asy] size(100); pair P,Q,R,M,NN; P = (0,0); Q = (0.5,0.9); R = (1,0); NN = (0.5,0); M = (Q+R)/2; draw(rightanglemark(Q,NN,P,2.5)); draw(M--P--Q--R--P); draw(Q--NN); l...
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Square $ABCD$ has sides of length 2. Set $S$ is the set of all line segments that have length 2 and whose endpoints are on adjacent sides of the square. The midpoints of the line segments in set $S$ enclose a region whose area to the nearest hundredth is $k$. Find $100k$.
Without loss of generality, let $(0,0)$, $(2,0)$, $(0,2)$, and $(2,2)$ be the vertices of the square. Suppose the endpoints of the segment lie on the two sides of the square determined by the vertex $(0,0)$. Let the two endpoints of the segment have coordinates $(x,0)$ and $(0,y)$. Because the segment has length 2, $x^...
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In $\triangle ABC,$ $AB=AC=25$ and $BC=23.$ Points $D,E,$ and $F$ are on sides $\overline{AB},$ $\overline{BC},$ and $\overline{AC},$ respectively, such that $\overline{DE}$ and $\overline{EF}$ are parallel to $\overline{AC}$ and $\overline{AB},$ respectively. What is the perimeter of parallelogram $ADEF$? [asy] real...
Since $\overline{DE} \parallel \overline{AC}$ and $\overline{EF} \parallel \overline{AB},$ triangles $\triangle BDE$ and $\triangle EFC$ are similar to $\triangle ABC$, and so they are also isosceles. That is, $BD = DE$ and $EF = FC.$ Then the perimeter of $ADEF$ is \[\begin{aligned} AD + DE + EF + AF &= AD + BD + FC ...
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Two sides of a triangle measure 4 cm and 9 cm. What is the greatest integer number of centimeters that could be the third side of this triangle?
Using the Triangle Inequality, we see that the third side must be smaller than the sum of the first two sides, or 13 cm. That means the greatest integer number of centimeters for the third side is $\boxed{12}.$
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What is the area, in square units, of a regular hexagon inscribed in a circle whose area is $324\pi$ square units? Express your answer in simplest radical form.
Note that since the area is $\pi r^2 = 324 \pi$, where $r$ is the radius, we must have $r=\sqrt{324}=18$. Thus the distance from the center of the hexagon to a vertex is $18$, and we can break up the hexagon into $6$ equilateral triangles, each of which has side length $18$. The area of an equilateral triangle of side ...
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A solid in the shape of a right circular cone is 4 inches tall and its base has a 3-inch radius. The entire surface of the cone, including its base, is painted. A plane parallel to the base of the cone divides the cone into two solids, a smaller cone-shaped solid $C$ and a frustum-shaped solid $F,$ in such a way that t...
Our original solid has volume equal to $V = \frac13 \pi r^2 h = \frac13 \pi 3^2\cdot 4 = 12 \pi$ and has surface area $A = \pi r^2 + \pi r \ell$, where $\ell$ is the slant height of the cone. Using the Pythagorean Theorem, we get $\ell = 5$ and $A = 24\pi$. Let $x$ denote the radius of the small cone. Let $A_c$ and $A_...
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Compute $\cos 270^\circ$.
Rotating the point $(1,0)$ about the origin by $270^\circ$ counterclockwise gives us the point $(0,-1)$, so $\cos 270^\circ = \boxed{0}$.
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In triangle $ABC$, $AB=125$, $AC=117$ and $BC=120$. The angle bisector of angle $A$ intersects $\overline{BC}$ at point $L$, and the angle bisector of angle $B$ intersects $\overline{AC}$ at point $K$. Let $M$ and $N$ be the feet of the perpendiculars from $C$ to $\overline{BK}$ and $\overline{AL}$, respectively. Find ...
Extend ${CM}$ and ${CN}$ such that they intersect line ${AB}$ at points $P$ and $Q$, respectively. Since ${BM}$ is the angle bisector of angle $B$, and ${CM}$ is perpendicular to ${BM}$, so $BP=BC=120$, and $M$ is the midpoint of ${CP}$. For the same reason, $AQ=AC=117$, and $N$ is the midpoint of ${CQ}$. Hence $MN=\fr...
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The circumference of a circle $A$ is 60 feet. How many feet long is $\widehat{BC}$? [asy] import markers; import olympiad; import geometry; import graph; size(150); defaultpen(linewidth(0.9)); draw(Circle(origin,1)); draw(dir(90)--origin--dir(30)); label("$B$",dir(90),N); label("$A$",origin,S); label("$C$",dir(30),E);...
Since $\widehat{BC}$ is $\frac{60}{360}=\frac16$ of the circle, $\widehat{BC}$ has length $\frac16(60)=\boxed{10}$ feet.
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Triangle $ABC$ with right angle at $C$, $\angle BAC < 45^\circ$ and $AB = 4$. Point $P$ on $\overline{AB}$ is chosen such that $\angle APC = 2\angle ACP$ and $CP = 1$. The ratio $\frac{AP}{BP}$ can be represented in the form $p + q\sqrt{r}$, where $p$, $q$, $r$ are positive integers and $r$ is not divisible by the squa...
Let $O$ be the circumcenter of $ABC$ and let the intersection of $CP$ with the circumcircle be $D$. It now follows that $\angle{DOA} = 2\angle ACP = \angle{APC} = \angle{DPB}$. Hence $ODP$ is isosceles and $OD = DP = 2$. Denote $E$ the projection of $O$ onto $CD$. Now $CD = CP + DP = 3$. By the Pythagorean Theorem, $OE...
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In convex quadrilateral $KLMN$ side $\overline{MN}$ is perpendicular to diagonal $\overline{KM}$, side $\overline{KL}$ is perpendicular to diagonal $\overline{LN}$, $MN = 65$, and $KL = 28$. The line through $L$ perpendicular to side $\overline{KN}$ intersects diagonal $\overline{KM}$ at $O$ with $KO = 8$. Find $MO$.
Let $\angle MKN=\alpha$ and $\angle LNK=\beta$. Note $\angle KLP=\beta$. Then, $KP=28\sin\beta=8\cos\alpha$. Furthermore, $KN=\frac{65}{\sin\alpha}=\frac{28}{\sin\beta} \Rightarrow 65\sin\beta=28\sin\alpha$. Dividing the equations gives\[\frac{65}{28}=\frac{28\sin\alpha}{8\cos\alpha}=\frac{7}{2}\tan\alpha\Rightarrow \t...
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A sphere is inscribed in a right cone with base radius $12$ cm and height $24$ cm, as shown. The radius of the sphere can be expressed as $a\sqrt{c} - a$ cm. What is the value of $a + c$? [asy] import three; size(120); defaultpen(linewidth(1)); pen dashes = linetype("2 2") + linewidth(1); currentprojection = orthograph...
Consider a cross-section of the cone that passes through the apex of the cone and the center of the circular base. It looks as follows: [asy] defaultpen(linewidth(1) + fontsize(10)); size(120); pen dashes = linetype("2 2") + linewidth(1); real r = 6*5^.5 - 6; pair A = (0,-24), O = (0,0), C = (0,-r), P = foot(C,(12,0),A...
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A round pizza is $\frac13$ of an inch thick and has a diameter of 12 inches. It is cut into 12 congruent pieces. What is the number of cubic inches in the volume of one piece? Express your answer in terms of $\pi$.
The entire pizza has radius 6 inches and volume $\pi (6^2)(1/3) = 12\pi$ cubic inches. One slice has 1/12th this volume, or $\boxed{\pi}$ cubic inches.
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The consecutive angles of a particular trapezoid form an arithmetic sequence. If the largest angle measures $120^{\circ}$, what is the measure of the smallest angle?
Let the angles be $a$, $a + d$, $a + 2d$, and $a + 3d$, from smallest to largest. Note that the sum of the measures of the smallest and largest angles is equal to the sum of the measures of the second smallest and second largest angles. This means that the sum of the measures of the smallest and largest angles is equal...
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A figure is constructed from unit cubes. Each cube shares at least one face with another cube. What is the minimum number of cubes needed to build a figure with the front and side views shown? [asy] /* AMC8 2003 #15 Problem */ draw((0,0)--(2,0)--(2,1)--(1,1)--(1,2)--(0,2)--cycle); draw((0,1)--(1,1)--(1,0)); draw((4,...
There are only two ways to construct a solid from three cubes so that each cube shares a face with at least one other: [asy] /* AMC8 2003 #15, p.1 Solution */ draw((0,0)--(3,0)--(3.5,.5)--(3.5,1.5)--(.5,1.5)--(0,1)--cycle); draw((0,1)--(3,1)); draw((1,0)--(1,1)--(1.5,1.5)); draw((2,0)--(2,1)--(2.5,1.5)); draw((3,0)--(3...
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Brad has a cylindrical barrel with radius 10 inches and height 15 inches. He wants to fill it from a well, using a bucket in the shape of a hemisphere with a radius of 10 inches. How many trips must Brad make to the well in order to fill the barrel?
We start by finding the volume of the bucket and the volume of the barrel. Let $r$ be ten inches. The bucket is half of a sphere of radius $r$, so the volume it can hold is \[ \frac{1}{2} \cdot \frac{4}{3} \pi r^3 = \frac{2}{3} \pi r^3 . \]On the other hand, the barrel is a cylinder of radius $r$ and height $15 \tex...
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A right circular cone has a base with radius $600$ and height $200\sqrt{7}.$ A fly starts at a point on the surface of the cone whose distance from the vertex of the cone is $125$, and crawls along the surface of the cone to a point on the exact opposite side of the cone whose distance from the vertex is $375\sqrt{2}.$...
The easiest way is to unwrap the cone into a circular sector. Center the sector at the origin with one radius on the positive $x$-axis and the angle $\theta$ going counterclockwise. The circumference of the base is $C=1200\pi$. The sector's radius (cone's sweep) is $R=\sqrt{r^2+h^2}=\sqrt{600^2+(200\sqrt{7})^2}=\sqrt{3...
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Let $R$ be a unit square region and $n \geq 4$ an integer. A point $X$ in the interior of $R$ is called n-ray partitional if there are $n$ rays emanating from $X$ that divide $R$ into $n$ triangles of equal area. How many points are $100$-ray partitional but not $60$-ray partitional? $\textbf{(A)}\ 1500 \qquad \textbf{...
There must be four rays emanating from $X$ that intersect the four corners of the square region. Depending on the location of $X$, the number of rays distributed among these four triangular sectors will vary. We start by finding the corner-most point that is $100$-ray partitional (let this point be the bottom-left-most...
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Find the number of square units in the area of the triangle. [asy]size(125); draw( (-10,-2) -- (2,10), Arrows); draw( (0,-2)-- (0,10) ,Arrows); draw( (5,0) -- (-10,0),Arrows); label("$l$",(2,10), NE); label("$x$", (5,0) , E); label("$y$", (0,-2) , S); filldraw( (-8,0) -- (0,8) -- (0,0) -- cycle, lightgray); dot( (-2,...
We first notice that the vertical and horizontal distances between the two points are both $4$, so the slope of the line which the two points are on must be $1$. We now find the length of the legs of the triangle. Since the slope of the line is one, we can add $2$ to both the $x$ and $y$-coordinates of $(-2,6)$ and get...
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A regular polygon has an exterior angle that measures $15$ degrees. How many sides does the polygon have?
The sum of the exterior angles of a polygon is $360^\circ$ as long as we take only one exterior angle per vertex. The polygon is regular, so all of the exterior angles have the same degree measure of $15$ degrees. If the polygon has $n$ sides, then the sum of the exterior angles is $15n=360$. So $n=24$ and the polygon ...
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Compute $\cos 210^\circ$.
Let $P$ be the point on the unit circle that is $210^\circ$ counterclockwise from $(1,0)$, and let $D$ be the foot of the altitude from $P$ to the $x$-axis, as shown below. [asy] pair A,C,P,O,D; draw((0,-1.2)--(0,1.2),p=black+1.2bp,Arrows(0.15cm)); draw((-1.2,0)--(1.2,0),p=black+1.2bp,Arrows(0.15cm)); A = (1,0); ...
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The triangle shown is an equilateral triangle with side length 12 cm. A side of the triangle is the diameter of the circle. If the sum of the areas of the two small shaded regions in square centimeters in simplest radical form is $a\pi - b\sqrt{c}$, what is $a+b+c$? [asy] import graph; size(2inch); pair A = dir(60); pa...
[asy] import graph; size(2inch); pair A = dir(60); pair B = dir(240); pair C = dir(0); pair D = dir(300); pair E = extension(A, C, B, D); fill(Arc((0,0), C, A)--cycle, gray); fill(Arc((0,0), B, D)--cycle, gray); draw(A--B); draw(A--E); draw(B--E); draw(Circle( (0,0), 1)); draw((0,0)--C); draw((0,0)--D); dot(A);dot(B);...
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Point $C(0,p)$ lies on the $y$-axis between $Q(0,12)$ and $O(0,0)$ as shown. Determine an expression for the area of $\triangle COB$ in terms of $p$. Your answer should be simplified as much as possible. [asy] size(5cm);defaultpen(fontsize(9)); pair o = (0, 0); pair q = (0, 12); pair b = (12, 0); pair a = (2, 12); pair...
Since $CO$ is perpendicular to $OB$, we can treat $CO$ as the height of $\triangle COB$ and $OB$ as the base. The area of $\triangle COB$ is $$\frac{1}{2}\times OB\times CO = \frac{1}{2}\times(12-0)\times(p-0)=\frac{1}{2}\times12\times p=\boxed{6p}.$$
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$ABCD$, a rectangle with $AB = 12$ and $BC = 16$, is the base of pyramid $P$, which has a height of $24$. A plane parallel to $ABCD$ is passed through $P$, dividing $P$ into a frustum $F$ and a smaller pyramid $P'$. Let $X$ denote the center of the circumsphere of $F$, and let $T$ denote the apex of $P$. If the volume ...
As we are dealing with volumes, the ratio of the volume of $P'$ to $P$ is the cube of the ratio of the height of $P'$ to $P$. Thus, the height of $P$ is $\sqrt [3]{8} = 2$ times the height of $P'$, and thus the height of each is $12$. Thus, the top of the frustum is a rectangle $A'B'C'D'$ with $A'B' = 6$ and $B'C' = 8$...
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In the diagram below, we have $\sin \angle RPQ = \frac{7}{25}$. What is $\sin \angle RPS$? [asy] pair R,P,Q,SS; SS = (-2,0); P = (0,0); Q = (2,0); R = rotate(aSin(7/25))*(1.5,0); dot("$S$",SS,S); dot("$Q$",Q,S); dot("$R$",R,N); dot("$P$",P,S); draw(Q--SS); draw(P--R); [/asy]
For any angle $x$, we have $\sin (180^\circ - x)=\sin x$, so $\sin RPS = \sin(180^\circ - \angle RPS) = \sin \angle RPQ = \boxed{\frac{7}{25}}$.
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In $\triangle{ABC}$ with side lengths $AB = 13$, $AC = 12$, and $BC = 5$, let $O$ and $I$ denote the circumcenter and incenter, respectively. A circle with center $M$ is tangent to the legs $AC$ and $BC$ and to the circumcircle of $\triangle{ABC}$. What is the area of $\triangle{MOI}$? $\textbf{(A)}\ 5/2\qquad\textbf{(...
Let the triangle have coordinates $(0,0),(12,0),(0,5).$ Then the coordinates of the incenter and circumcenter are $(2,2)$ and $(6,2.5),$ respectively. If we let $M=(x,x),$ then $x$ satisfies\[\sqrt{(2.5-x)^2+(6-x)^2}+x=6.5\]\[2.5^2-5x+x^2+6^2-12x+x^2=6.5^2-13x+x^2\]\[x^2=(5+12-13)x\]\[x\neq 0\implies x=4.\]Now the area...
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A square piece of paper has sides of length $100$. From each corner a wedge is cut in the following manner: at each corner, the two cuts for the wedge each start at a distance $\sqrt{17}$ from the corner, and they meet on the diagonal at an angle of $60^{\circ}$ (see the figure below). The paper is then folded up along...
[asy] import three; import math; import cse5; size(500); pathpen=blue; real r = (51^0.5-17^0.5)/200, h=867^0.25/100; triple A=(0,0,0),B=(1,0,0),C=(1,1,0),D=(0,1,0); triple F=B+(r,-r,h),G=(1,-r,h),H=(1+r,0,h),I=B+(0,0,h); draw(B--F--H--cycle); draw(B--F--G--cycle); draw(G--I--H); draw(B--I); draw(A--B--C--D--cycle); tri...
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The nine points of this grid are equally spaced horizontally and vertically. The distance between two neighboring points is 1 unit. What is the area, in square units, of the region where the two triangles overlap? [asy] size(80); dot((0,0)); dot((0,1));dot((0,2));dot((1,0));dot((1,1));dot((1,2));dot((2,0));dot((2,1)...
We color one of the triangles blue, and draw three blue segments connecting its points of intersection with the other triangle. [asy] size(80); dot((0,0)); dot((0,1));dot((0,2));dot((1,0));dot((1,1));dot((1,2));dot((2,0));dot((2,1));dot((2,2)); draw((0,0)--(2,1)--(1,2)--cycle, blue+linewidth(0.6)); draw((2,2)--(0,1)...
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Two sectors of a circle of radius $12$ are placed side by side, as shown. Determine the $\textit{area}$ of figure $ABCD.$ [asy] draw((0,0)--(12,0)..(10.3923,6)..(6,10.3923)--(-6,10.3923)..(-4.3923,4.3923)..(0,0),black+linewidth(1)); draw((0,0)--(6,10.3923),black+linewidth(1)+dashed); label("$A$",(-6,10.3923),NW); label...
Each of sector $ABD$ and $BDC$ is one-sixth of a full circle of radius $12,$ so each has area one-sixth of the area of a circle of radius $12.$ Therefore, each sector has area $$\frac{1}{6}(\pi(12^2))=\frac{1}{6}(144\pi)=24\pi.$$ Thus, the area of figure $ABCD$ is $2( 24\pi)=\boxed{48\pi}.$
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An equilateral triangle has two vertices at $(0,5)$ and $(8,5)$. If the third vertex is in the first quadrant, what is the y-coordinate? Express your answer in simplest radical form. [asy] draw((-1,0)--(11,0),Arrows); draw((0,-1)--(0,12),Arrows); for(int i=0;i<11;++i) {draw((i,-0.1)--(i,0.1));} for(int j=0;j<11;++j) {d...
To begin this problem, we first notice that the side length of this equilateral triangle is $8$ (the distance between the two points given). We then consider the altitude of an equilateral triangle with side length $8$. If we draw an equilateral triangle and its altitude, we notice that the altitude splits the equilate...
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Acute-angled $\triangle ABC$ is inscribed in a circle with center at $O$; $\stackrel \frown {AB} = 120^\circ$ and $\stackrel \frown {BC} = 72^\circ$. A point $E$ is taken in minor arc $AC$ such that $OE$ is perpendicular to $AC$. Then the ratio of the magnitudes of $\angle OBE$ and $\angle BAC$ is: $\textbf{(A)}\ \frac...
[asy] draw(circle((0,0),1)); dot((-1,0)); pair A=(-1,0),B=(0.5,0.866),C=(0.978,-0.208),O=(0,0),E=(-0.105,-0.995); label("A",(-1,0),W); dot((0.5,0.866)); label("B",(0.5,0.866),NE); dot((0.978,-0.208)); label("C",(0.978,-0.208),SE); dot((0,0)); label("O",(0,0),NE); dot(E); label("E",E,S); draw(A--B--C--A); draw(E--O); [...
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What is the area, in square units, of a triangle whose vertices are at $(4, -1)$, $(10, 3)$ and $(4, 5)$?
Notice how two of the points, $(4,-1)$ and $(4,5)$, lie on the same line parallel through the $y$-axis with $x$-intercept $(4,0)$. Let these points lie on the base of the triangle, so the base has length $5-(-1)=6$. The height is the perpendicular distance from $(10,3)$ to this line, which is $10-4=6$. The area is t...
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Two identical rectangular crates are packed with cylindrical pipes, using different methods. Each pipe has diameter 10 cm. A side view of the first four rows of each of the two different methods of packing is shown below. [asy] draw(circle((1,1),1),black+linewidth(1)); draw(circle((3,1),1),black+linewidth(1)); draw(c...
In Crate A, we have 20 rows of 10 pipes packed directly on top of each other. So the height of the packing is 20 times the diameter of a single pipe, or 200 cm. In Crate B, draw a horizontal line through the centers of the 9 or 10 pipes in each row. By symmetry, the distance between each consecutive pair of these 21 l...
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An $\textit{annulus}$ is the region between two concentric circles. The concentric circles in the figure have radii $b$ and $c$, with $b>c$. Let $\overline{OX}$ be a radius of the larger circle, let $\overline{XZ}$ be tangent to the smaller circle at $Z$, and let $\overline{OY}$ be the radius of the larger circle that ...
The area of the annulus is the difference between the areas of the two circles, which is $\pi b^2 -\pi c^2$. Because the tangent $\overline{XZ}$ is perpendicular to the radius $\overline{OZ}$, $b^2 - c^2 = a^2$, so the area is $\boxed{\pi a^2}$.
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In $\triangle ABC$, we have $AC=BC=7$ and $AB=2$. Suppose that $D$ is a point on line $AB$ such that $B$ lies between $A$ and $D$ and $CD=8$. What is $BD$?
Let $\overline{CH}$ be an altitude of $\triangle ABC$. Applying the Pythagorean Theorem to $\triangle CHB$ and to $\triangle CHD$ produces \[ 8^2 - (BD +1)^2 = CH^2 = 7^2 - 1^2 = 48, \quad \text{so} \quad (BD+1)^2 = 16. \] Thus $BD = \boxed{3}$. [asy] unitsize(0.5cm); pair A,B,C,D,H; A=(0,0); H=(1,0); B=(2,0); D=(5,0...
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An 8-foot by 10-foot floor is tiled with square tiles of size 1 foot by 1 foot. Each tile has a pattern consisting of four white quarter circles of radius 1/2 foot centered at each corner of the tile. The remaining portion of the tile is shaded. How many square feet of the floor are shaded? [asy] fill((5,5)--(5,-5)--(-...
The four white quarter circles in each tile have the same area as a whole circle of radius $1/2$, that is, $\pi(1/2)^2 = \pi/4$ square feet. So the area of the shaded portion of each tile is $ 1 - \pi/4$ square feet. Since there are $8\cdot 10 = 80$ tiles in the entire floor, the area of the total shaded region in squa...
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In $\triangle PQR$, point $T$ is on side $QR$ such that $QT=6$ and $TR=10$. What is the ratio of the area of $\triangle PQT$ to the area of $\triangle PTR$? [asy] size(6cm); pair q = (0, 0); pair t = (6, 0); pair r = (16, 0); pair p = (4, 8); draw(p--q--r--cycle--t); label("$P$", p, N); label("$Q$", q, SW); label("$T$"...
Construct the altitude of $\triangle PQT$ from $P$ to $QT$. Let the length of the altitude be $h$. [asy] size(6cm); pair q = (0, 0); pair t = (6, 0); pair r = (16, 0); pair p = (4, 8); pair f = foot(p, q, r); draw(p--q--r--cycle--t);draw(p--f, dashed); label("$P$", p, N); label("$Q$", q, SW); label("$T$", t, S); label(...
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Let $u$ and $v$ be integers satisfying $0 < v < u$. Let $A = (u,v)$, let $B$ be the reflection of $A$ across the line $y = x$, let $C$ be the reflection of $B$ across the y-axis, let $D$ be the reflection of $C$ across the x-axis, and let $E$ be the reflection of $D$ across the y-axis. The area of pentagon $ABCDE$ is $...
[asy] pointpen = black; pathpen = linewidth(0.7) + black; size(180); pair A=(11,10), B=(10,11), C=(-10, 11), D=(-10, -11), E=(10, -11); D(D(MP("A\ (u,v)",A,(1,0)))--D(MP("B",B,N))--D(MP("C",C,N))--D(MP("D",D))--D(MP("E",E))--cycle); D((-15,0)--(15,0),linewidth(0.6),Arrows(5)); D((0,-15)--(0,15),linewidth(0.6),Arrows(5)...
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Two concentric circles are centered at point P. The sides of a 45 degree angle at P form an arc on the smaller circle that is the same length as an arc on the larger circle formed by the sides of a 36 degree angle at P. What is the ratio of the area of the smaller circle to the area of the larger circle? Express your ...
Let $C_1$ and $C_2$ be the circumferences of the smaller and larger circle, respectively. The length of the $45^\circ$ arc on the smaller circle is $\left(\frac{45^\circ}{360^\circ}\right)C_1$, and the length of the $36^\circ$ arc on the larger circle is $\left(\frac{36^\circ}{360^\circ}\right)C_2$. Setting these two...
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Two different points, $C$ and $D$, lie on the same side of line $AB$ so that $\triangle ABC$ and $\triangle BAD$ are congruent with $AB = 9$, $BC=AD=10$, and $CA=DB=17$. The intersection of these two triangular regions has area $\tfrac mn$, where $m$ and $n$ are relatively prime positive integers. Find $m+n$.
[asy] unitsize(10); pair A = (0,0); pair B = (9,0); pair C = (15,8); pair D = (-6,8); pair E = (-6,0); draw(A--B--C--cycle); draw(B--D--A); label("$A$",A,dir(-120)); label("$B$",B,dir(-60)); label("$C$",C,dir(60)); label("$D$",D,dir(120)); label("$E$",E,dir(-135)); label("$9$",(A+B)/2,dir(-90)); label("$10$",(D+A)/2,di...
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At the MP Donut Hole Factory, Niraek, Theo, and Akshaj are coating spherical donut holes in powdered sugar. Niraek's donut holes have radius 6 mm, Theo's donut holes have radius 8 mm, and Akshaj's donut holes have radius 10 mm. All three workers coat the surface of the donut holes at the same rate and start at the sa...
The amount of powdered sugar on a given donut hole is given by the surface area of the donut hole. The surface area of a sphere with radius $r$ is $4\pi r^2$, so Niraek's donut holes each have surface area $4\pi \cdot 6^2 = 144\pi$ square millimeters. Similarly, Theo's donut holes each have surface area $4\pi \cdot 8...
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A sphere is inscribed in a cube. What is the ratio of the volume of the inscribed sphere to the volume of the cube? Express your answer as a common fraction in terms of $\pi$.
[asy] size(60); draw(Circle((6,6),4.5)); draw((10.5,6)..(6,6.9)..(1.5,6),linetype("2 4")); draw((10.5,6)..(6,5.1)..(1.5,6)); draw((0,0)--(9,0)--(9,9)--(0,9)--cycle); draw((0,9)--(3,12)--(12,12)--(9,9)); draw((12,12)--(12,3)--(9,0)); draw((0,0)--(3,3)--(12,3),dashed); draw((3,3)--(3,12),dashed); [/asy] Let the side len...
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Let $A_0=(0,0)$. Distinct points $A_1,A_2,\dots$ lie on the $x$-axis, and distinct points $B_1,B_2,\dots$ lie on the graph of $y=\sqrt{x}$. For every positive integer $n,\ A_{n-1}B_nA_n$ is an equilateral triangle. What is the least $n$ for which the length $A_0A_n\geq100$? $\textbf{(A)}\ 13\qquad \textbf{(B)}\ 15\qqua...
Let $a_n=|A_{n-1}A_n|$. We need to rewrite the recursion into something manageable. The two strange conditions, $B$'s lie on the graph of $y=\sqrt{x}$ and $A_{n-1}B_nA_n$ is an equilateral triangle, can be compacted as follows:\[\left(a_n\frac{\sqrt{3}}{2}\right)^2=\frac{a_n}{2}+a_{n-1}+a_{n-2}+\cdots+a_1\]which uses $...
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How many different triangles can be formed having a perimeter of 7 units if each side must have integral length?
Let $a,b,$ and $c$ represent the three side lengths of the triangle. The perimeter is $a+b+c=7,$ so $b+c=7-a$. We know by the Triangle Inequality that the sum of two side lengths of a triangle must be greater than the third side length. If we focus on the variable $a$, we have \[b+c>a\quad\Rightarrow \quad 7-a>a\quad\R...
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Compute $\tan 0^\circ$.
Rotating the point $(1,0)$ about the origin by $0^\circ$ counterclockwise gives us the point $(1,0)$, so $\tan 0^\circ = \frac{\sin 0^\circ}{\cos 0^\circ} = \frac{0}{1} = \boxed{0}$.
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The hypotenuse of a right triangle whose legs are consecutive whole numbers is 29 units. What is the sum of the lengths of the two legs?
Let's call the length of the shorter leg $x$. Then the length of the longer leg is $x + 1$. Using the Pythagorean Theorem, we write the equation $x^2 + (x + 1)^2 = 29^2$ and solve for $x$. Expanding $(x + 1)^2$, we get $x ^2 + x^2 + 2x + 1 = 841$. This can be simplified to $2x^2 + 2x = 840$, or $x^2 + x = 420$. Factori...
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In the diagram, $PQ$ and $RS$ are diameters of a circle with radius 4. If $PQ$ and $RS$ are perpendicular, what is the area of the shaded region? [asy] size(120); import graph; fill((-1,-1)--(-1,1)--(1,1)--(1,-1)--cycle,mediumgray); fill(Arc((0,0),sqrt(2),45,135)--cycle,mediumgray);fill(Arc((0,0),sqrt(2),225,315)--cy...
Diameters $PQ$ and $RS$ cross at the center of the circle, which we call $O$. The area of the shaded region is the sum of the areas of $\triangle POS$ and $\triangle ROQ$ plus the sum of the areas of sectors $POR$ and $SOQ$. Each of $\triangle POS$ and $\triangle ROQ$ is right-angled and has its two perpendicular sid...
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In the circle with center $O$, the measure of $\angle RIP$ is $36^\circ$ and $OR=10$ cm. Find the number of centimeters in the length of arc $RP$. Express your answer in terms of $\pi$. [asy] draw((1,0)..(0,1)..(-1,0)..(0,-1)..cycle); draw((0,0)--(4/5,3/5)--(-1,0)--(4/5,-3/5)--cycle); label("$O$",(0,0),W); label("$I$",...
Since $\angle RIP$ is inscribed in arc $RP$, the measure of arc $RP$ is $2\angle RIP = 72^\circ$. Therefore, arc $RP$ is $\frac{72}{360} =\frac15$ of the circumference of the whole circle. The circle's circumference is $2OR\pi = 20\pi$ cm, so the length of arc $RP$ is $\frac15\cdot 20\pi = \boxed{4\pi}$ cm.
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In the diagram, if $\angle PQR = 48^\circ$, what is the measure of $\angle PMN$? [asy] size(6cm); pair p = (0, 0); pair m = dir(180 - 24); pair n = dir(180 + 24); pair r = 1.3 * dir(24); pair q = 2 * 1.3 * Cos(48) * dir(-24); label("$M$", m, N); label("$R$", r, N); label("$P$", p, 1.5 * S); label("$N$", n, S); label...
In $\triangle PQR$, since $PR=RQ$, then $\angle RPQ=\angle PQR = 48^\circ$. Since $\angle MPN$ and $\angle RPQ$ are opposite angles, we have $\angle MPN = \angle RPQ=48^\circ$. In $\triangle PMN$, $PM=PN$, so $\angle PMN = \angle PNM$. Therefore, $$\angle PMN = \frac{1}{2}(180^\circ - \angle MPN) = \frac{1}{2}(180^\...
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A block of wood has the shape of a right circular cylinder with radius $6$ and height $8$, and its entire surface has been painted blue. Points $A$ and $B$ are chosen on the edge of one of the circular faces of the cylinder so that $\overarc{AB}$ on that face measures $120^\text{o}$. The block is then sliced in half al...
Label the points where the plane intersects the top face of the cylinder as $C$ and $D$, and the center of the cylinder as $O$, such that $C,O,$ and $A$ are collinear. Let $T$ be the center of the bottom face, and $M$ the midpoint of $\overline{AB}$. Then $OT=4$, $TM=3$ (because of the 120 degree angle), and so $OM=5$....
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Rectangle $ABCD$ has sides $\overline {AB}$ of length 4 and $\overline {CB}$ of length 3. Divide $\overline {AB}$ into 168 congruent segments with points $A=P_0, P_1, \ldots, P_{168}=B$, and divide $\overline {CB}$ into 168 congruent segments with points $C=Q_0, Q_1, \ldots, Q_{168}=B$. For $1 \le k \le 167$, draw the ...
[asy] real r = 0.35; size(220); pointpen=black;pathpen=black+linewidth(0.65);pen f = fontsize(8); pair A=(0,0),B=(4,0),C=(4,3),D=(0,3); D(A--B--C--D--cycle); pair P1=A+(r,0),P2=A+(2r,0),P3=B-(r,0),P4=B-(2r,0); pair Q1=C-(0,r),Q2=C-(0,2r),Q3=B+(0,r),Q4=B+(0,2r); D(A--C);D(P1--Q1);D(P2--Q2);D(P3--Q3);D(P4--Q4); MP("A",A,...
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A bowling ball cannot weigh more than 16 pounds and must have a diameter of $8 \frac{1}{2}$ inches. How many square inches are in the surface area of a bowling ball before the finger holes are drilled? Express your answer as a common fraction in terms of $\pi$.
The surface area of a sphere with radius $r$ is \[4\pi r^2.\] The sphere in question has diameter $8\frac{1}{2}=\frac{17}{2}$, radius $\frac{17}{4}$, and surface area \[4\pi\left(\frac{17}{4}\right)^2 = \frac{17^2}{4}\pi = \boxed{\frac{289\pi}{4}}.\]
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