problem
stringlengths
16
4.31k
level
stringclasses
6 values
type
stringclasses
7 values
solution
stringlengths
29
6.77k
index
int64
0
25.9k
Parallelogram $ABCD$ with $A(2,5)$, $B(4,9)$, $C(6,5)$, and $D(4,1)$ is reflected across the $x$-axis to $A'B'C'D'$ and then $A'B'C'D'$ is reflected across the line $y=x+1$ to $A''B''C''D''$. This is done such that $D'$ is the image of $D$, and $D''$ is the image of $D'$. What is the ordered pair of $D''$ in the coordi...
Level 5
Geometry
Reflecting a point across the $x$-axis multiplies its $y$-coordinate by $-1$. Therefore, $D'=(4,-1)$. To reflect $D'$ across the line $y=x+1$, we first translate both the line and the point down one unit so that the equation of the translated line is $y=x$ and the coordinates of the translated point are $(4,-2)$. To...
659
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...
Level 5
Geometry
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...
308
Two circles of radius 2 are centered at $(2,0)$ and at $(0,2)$. What is the area of the intersection of the interiors of the two circles? Express your answer in fully expanded form in terms of $\pi$.
Level 5
Geometry
The two circles intersect at $(0,0)$ and $(2,2)$, as shown. [asy] unitsize(1cm); linewidth(1); draw((-2.5,0)--(5,0),Arrow); draw((0,-2.5)--(0,5),Arrow); draw((-2.5,0)--(5,0),linewidth(0.6)); draw((0,-2.5)--(0,5),linewidth(0.6)); label("$x$",(5,0),S); label("$y$",(0,5),E); for (int i=0; i<6; ++i) { draw((-2+i,-0.2)--(-...
1,136
Given that $O$ is a regular octahedron, that $C$ is the cube whose vertices are the centers of the faces of $O,$ and that the ratio of the volume of $O$ to that of $C$ is $\frac mn,$ where $m$ and $n$ are relatively prime integers, find $m+n.$
Level 5
Geometry
[asy] import three; currentprojection = perspective(4,-15,4); defaultpen(linewidth(0.7)); draw(box((-1,-1,-1),(1,1,1))); draw((-3,0,0)--(0,0,3)--(0,-3,0)--(-3,0,0)--(0,0,-3)--(0,-3,0)--(3,0,0)--(0,0,-3)--(0,3,0)--(0,0,3)--(3,0,0)--(0,3,0)--(-3,0,0)); [/asy] Let the side of the octahedron be of length $s$. Let the verti...
6,094
Quadrilateral $ABCD$ has right angles at $B$ and $D$, and $AC=3$. If $ABCD$ has two sides with distinct integer lengths, then what is the area of $ABCD$? Express your answer in simplest radical form.
Level 5
Geometry
Triangles $\triangle ABC$ and $\triangle ADC$ are both right and share hypotenuse $AC$, which has length $3$. Thus we have $$AB^2+BC^2 = AD^2+DC^2 = 3^2 = 9.$$The only possible integer values for $AB,$ $BC,$ $AD,$ or $DC$ are $1$ and $2$. Thus we may assume that one leg of $\triangle ABC$ has length $1$ and one leg of ...
910
Compute $\cos 150^\circ$.
Level 3
Geometry
Let $P$ be the point on the unit circle that is $150^\circ$ 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= (0...
626
In triangle $ABC$, $AB = 16$, $AC = 24$, $BC = 19$, and $AD$ is an angle bisector. Find the ratio of the area of triangle $ABD$ to the area of triangle $ACD$. (Express your answer as a fraction in lowest terms.)
Level 4
Geometry
The ratio of the area of triangle $ABD$ to the area of triangle $ACD$ is $BD/CD$. By the angle bisector theorem, $BD/CD = AB/AC = 16/24 = \boxed{\frac{2}{3}}$.
779
An ice cream cone has radius 1 inch and height 4 inches, What is the number of inches in the radius of a sphere of ice cream which has the same volume as the cone?
Level 2
Geometry
A cone with radius $r$ and height $h$ has volume $\frac{1}{3}\pi r^2 h$; here, our cone has volume $\frac{1}{3}\pi (1^2)(4)=\frac{4}{3}\pi$. A sphere with radius $r$ has volume $\frac{4}{3}\pi r^3$, so we set up the equation \[\frac{4}{3}\pi r^3=\frac{4}{3}\pi.\] Solving for $r$ yields $r^3=1$, so $r = 1$. The sphere...
378
In triangle $XYZ$, we have $\angle Z = 90^\circ$, $XY = 10$, and $YZ = \sqrt{51}$. What is $\tan X$?
Level 2
Geometry
[asy] pair X,Y,Z; Z = (0,0); Y = (sqrt(51),0); X = (0,7); draw(X--Y--Z--X); draw(rightanglemark(Y,Z,X,15)); label("$X$",X,NE); label("$Y$",Y,SE); label("$Z$",Z,SW); label("$10$",(X+Y)/2,NE); label("$\sqrt{51}$",(Z+Y)/2,S); [/asy] Because this is a right triangle, $\tan X = \frac{YZ}{XZ}$. Using the Pythag...
425
The radius of the inscribed circle is 6 cm. What is the number of centimeters in the length of $\overline{AB}$? Express your answer in simplest radical form. [asy] import olympiad; import geometry; size(150); defaultpen(linewidth(0.8)); draw((sqrt(3),0)--origin--(0,1)--cycle); real r1 = (sqrt(3) - 1)/2; draw(Circle((r1...
Level 5
Geometry
Define points $C$, $D$, $E$, $F$ and $O$ as shown in the figure. Triangles $BCO$ and $BFO$ are right triangles that share a hypotenuse, and $CO=6\text{ cm}=OF$. By the hypotenuse-leg congruency theorem, triangles $BCO$ and $BFO$ are congruent. Therefore, angles $CBO$ and $FBO$ each measure 30 degrees, so angle $BOC$...
176
Two circles are drawn in a 12-inch by 14-inch rectangle. Each circle has a diameter of 6 inches. If the circles do not extend beyond the rectangular region, what is the greatest possible distance (in inches) between the centers of the two circles?
Level 5
Geometry
Suppose we put the two circles in opposite corners of the rectangle so that the circles are tangent to the sides of the rectangle, and they are diagonally across from each other. Then the center of each circle is 3 inches in from each side of the rectangle that it touches. Now imagine a rectangle that has opposite corn...
495
Let $ABCDEF$ be a regular hexagon, and let $G,H,I$ be the midpoints of sides $AB,CD,EF$ respectively. If the area of $\triangle GHI$ is $225$, what is the area of hexagon $ABCDEF$?
Level 5
Geometry
We begin with a diagram of the given information: [asy] size(4cm); real x=sqrt(3); pair d=(2,0); pair c=(1,x); pair b=(-1,x); pair a=-d; pair f=-c; pair e=-b; pair g=(a+b)/2; pair h=(c+d)/2; pair i=(e+f)/2; draw(a--b--c--d--e--f--a); dot(a); dot(b); dot(c); dot(d); dot(e); dot(f); dot(g); dot(h); dot(i); draw(g--h--i--...
472
Let $\triangle PQR$ be a triangle in the plane, and let $S$ be a point outside the plane of $\triangle PQR$, so that $SPQR$ is a pyramid whose faces are all triangles. Suppose that every edge of $SPQR$ has length $18$ or $41$, but no face of $SPQR$ is equilateral. Then what is the surface area of $SPQR$?
Level 5
Geometry
Since all edges of pyramid $SPQR$ have length $18$ or $41$, each triangular face must be isosceles: either $18$-$18$-$41$ or $18$-$41$-$41$. But the first of these two sets of side lengths violates the triangle inequality, since $18+18<41$. Therefore, every face of $SPQR$ must have sides of lengths $18,$ $41,$ and $41$...
612
Two boards, one four inches wide and the other six inches wide, are nailed together to form an X. The angle at which they cross is 60 degrees. If this structure is painted and the boards are separated what is the area of the unpainted region on the four-inch board? (The holes caused by the nails are negligible.) Expres...
Level 5
Geometry
Note that the unpainted region forms a parallelogram with heights between bases of 4 inches and 6 inches and with one angle 60 degree, as shown. [asy] size(150); unitsize(7.5,7.5); import olympiad; draw(6dir(150)--15dir(-30),dashed); draw((6dir(150)+12/sqrt(3)*dir(30))--(15dir(-30)+12/sqrt(3)*dir(30)),dashed); draw(6...
533
Three of the edges of a cube are $\overline{AB}, \overline{BC},$ and $\overline{CD},$ and $\overline{AD}$ is an interior diagonal. Points $P, Q,$ and $R$ are on $\overline{AB}, \overline{BC},$ and $\overline{CD},$ respectively, so that $AP = 5, PB = 15, BQ = 15,$ and $CR = 10.$ What is the area of the polygon that is t...
Level 5
Geometry
[asy] import three; size(280); defaultpen(linewidth(0.6)+fontsize(9)); currentprojection=perspective(30,-60,40); triple A=(0,0,0),B=(20,0,0),C=(20,0,20),D=(20,20,20); triple P=(5,0,0),Q=(20,0,15),R=(20,10,20),Pa=(15,20,20),Qa=(0,20,5),Ra=(0,10,0); draw(box((0,0,0),(20,20,20))); draw(P--Q--R--Pa--Qa--Ra--cycle,linewidth...
6,042
In the diagram, $P$ is on $RS$ so that $QP$ bisects $\angle SQR$. Also, $PQ=PR$, $\angle RSQ=2y^\circ$, and $\angle RPQ=3y^\circ$. What is the measure, in degrees, of $\angle RPQ$? [asy] // C14 import olympiad; size(7cm); real x = 50; real y = 20; pair q = (1, 0); pair r = (0, 0); pair p = intersectionpoints((10 * ...
Level 3
Geometry
Since $RPS$ is a straight line, then $\angle SPQ = 180^\circ - \angle RPQ = 180^\circ - 3y^\circ$. Using the angles in $\triangle PQS$, we have $\angle PQS + \angle QSP + \angle SPQ = 180^\circ$. Thus, $x^\circ+2y^\circ + (180^\circ - 3y^\circ) = 180^\circ$ or $x-y+180 = 180$ or $x=y$. (We could have instead looked a...
811
A cube has eight vertices (corners) and twelve edges. A segment, such as $x$, which joins two vertices not joined by an edge is called a diagonal. Segment $y$ is also a diagonal. How many diagonals does a cube have? [asy] /* AMC8 1998 #17 Problem */ pair A=(0,48), B=(0,0), C=(48,0), D=(48,48); pair E=(24,72), F=(24,24)...
Level 3
Geometry
There are two diagonals, such as $x$, in each of the six faces for a total of twelve face diagonals. There are also four space diagonals, such as $y$, which are within the cube. This makes a total of $\boxed{16}$.
34
An $8$-cm-by-$8$-cm square is partitioned as shown. Points $A$ and $B$ are the midpoints of two opposite sides of the square. What is the area of the shaded region? [asy] draw((0,0)--(10,0)); draw((10,0)--(10,10)); draw((10,10)--(0,10)); draw((0,0)--(0,10)); draw((0,0)--(5,10)); draw((5,10)--(10,0)); draw((0,10)--(5,0...
Level 2
Geometry
Draw a line segment from $A$ to $B,$ cutting the shaded diamond region in half. Next, draw the altitude from point $E$ to segment $AB.$ The new figure is shown below: [asy] draw((0,0)--(10,0)); draw((10,0)--(10,10)); draw((10,10)--(0,10)); draw((0,0)--(0,10)); draw((0,0)--(5,10)); draw((5,10)--(10,0)); draw((0,10)--(5,...
833
In the adjoining figure, $CD$ is the diameter of a semicircle with center $O$. Point $A$ lies on the extension of $DC$ past $C$; point $E$ lies on the semicircle, and $B$ is the point of intersection (distinct from $E$) of line segment $AE$ with the semicircle. If length $AB$ equals length $OD$, and the measure of $\...
Level 5
Geometry
Draw $BO$. Let $y = \angle BAO$. Since $AB = OD = BO$, triangle $ABO$ is isosceles, so $\angle BOA = \angle BAO = y$. Angle $\angle EBO$ is exterior to triangle $ABO$, so $\angle EBO = \angle BAO + \angle BOA = y + y = 2y$. [asy] import graph; unitsize(2 cm); pair O, A, B, C, D, E; O = (0,0); C = (-1,0); D = (1,...
854
The measures of angles $A$ and $B$ are both positive, integer numbers of degrees. The measure of angle $A$ is a multiple of the measure of angle $B$, and angles $A$ and $B$ are complementary angles. How many measures are possible for angle $A$?
Level 5
Geometry
The given information tells us that $A = 90^\circ -B$ and $A=kB$ for some $k\ge1$. Therefore, we have $kB = 90^\circ - B$. This simplifies to $(k+1)B=90^\circ$. $k+1$ can be any factor of $90$ except one, since $k+1\ge2$. $90=2\cdot3^2\cdot5$ has $2\cdot3\cdot2=12$ factors, so there are 11 possible values of $k$. Each...
544
In triangle $ABC$, $A'$, $B'$, and $C'$ are on the sides $BC$, $AC$, and $AB$, respectively. Given that $AA'$, $BB'$, and $CC'$ are concurrent at the point $O$, and that $\frac{AO}{OA'}+\frac{BO}{OB'}+\frac{CO}{OC'}=92$, find $\frac{AO}{OA'}\cdot \frac{BO}{OB'}\cdot \frac{CO}{OC'}$.
Level 5
Geometry
Let $K_A=[BOC], K_B=[COA],$ and $K_C=[AOB].$ Due to triangles $BOC$ and $ABC$ having the same base,\[\frac{AO}{OA'}+1=\frac{AA'}{OA'}=\frac{[ABC]}{[BOC]}=\frac{K_A+K_B+K_C}{K_A}.\]Therefore, we have\[\frac{AO}{OA'}=\frac{K_B+K_C}{K_A}\]\[\frac{BO}{OB'}=\frac{K_A+K_C}{K_B}\]\[\frac{CO}{OC'}=\frac{K_A+K_B}{K_C}.\]Thus, w...
6,022
Consider the parallelogram with vertices $(10,45)$, $(10,114)$, $(28,153)$, and $(28,84)$. A line through the origin cuts this figure into two congruent polygons. The slope of the line is $m/n,$ where $m$ and $n$ are relatively prime positive integers. Find $m+n$.
Level 5
Geometry
Let the first point on the line $x=10$ be $(10,45+a)$ where a is the height above $(10,45)$. Let the second point on the line $x=28$ be $(28, 153-a)$. For two given points, the line will pass the origin if the coordinates are proportional (such that $\frac{y_1}{x_1} = \frac{y_2}{x_2}$). Then, we can write that $\frac{4...
6,047
Let $AB$ be a diameter of a circle centered at $O$. Let $E$ be a point on the circle, and let the tangent at $B$ intersect the tangent at $E$ and $AE$ at $C$ and $D$, respectively. If $\angle BAE = 43^\circ$, find $\angle CED$, in degrees. [asy] import graph; unitsize(2 cm); pair O, A, B, C, D, E; O = (0,0); A = ...
Level 4
Geometry
Both angles $\angle BAD$ and $\angle CBE$ subtend arc $BE$, so $\angle CBE = \angle BAE = 43^\circ$. Triangle $BCE$ is isosceles with $BC = CE$, since these are tangent from the same point to the same circle, so $\angle CEB = \angle CBE = 43^\circ$. Finally, $\angle AEB = 90^\circ$ since $AB$ is a diameter, so $\angl...
147
Regular hexagon $ABCDEF$ has vertices $A$ and $C$ at $(0,0)$ and $(7,1)$, respectively. What is its area?
Level 5
Geometry
Diagonals $\overline{AC}$, $\overline{CE}$, $\overline{EA}$, $\overline{AD}$, $\overline{CF}$, and $\overline{EB}$ divide the hexagon into twelve congruent 30-60-90 triangles, six of which make up equilateral $\triangle ACE$. [asy] unitsize(0.5 cm); pair A, B, C, D, E, F, G; A = (0,0); C = (7,1); E = rotate(60)*(C);...
873
Triangle $ABC$ is isosceles with angle $B$ congruent to angle $C$. The measure of angle $C$ is four times the measure of angle $A$. What is the number of degrees in the measure of angle $B$?
Level 1
Geometry
Let $x$ be the number of degrees in $\angle A$. Then $\angle C=4x^\circ$, and $\angle B$ is also $4x^\circ$ (since $\angle B$ is congruent to $\angle C$). Since the sum of angles in a triangle is $180^\circ$, we have $$x + 4x + 4x = 180,$$ which we can solve for $x=20$. Therefore, $\angle B = 4\cdot 20 = \boxed{80}$ d...
749
In the figure, triangles $ABC$ and $BCD$ are equilateral triangles. What is the value of $AD \div BC$ when expressed in simplest radical form? [asy] draw((0,0)--(5,8.7)--(10,0)--cycle); draw((10,0)--(15,8.7)--(5,8.7)); label("$A$",(0,0),SW); label("$B$",(5,8.7),N); label("$C$",(10,0),SE); label("$D$",(15,8.7),NE); [/a...
Level 3
Geometry
Let $BC = s$. We can see that $AD$ consists of the altitudes from $A$ and $D$ to $BC$, each of which has length $s\sqrt{3}/2$. Thus, $AD = s\sqrt{3}$. Therefore, $AD\div BC = s\sqrt{3}/s = \boxed{\sqrt{3}}$.
789
The points $B(1, 1)$, $I(2, 4)$ and $G(5, 1)$ are plotted in the standard rectangular coordinate system to form triangle $BIG$. Triangle $BIG$ is translated five units to the left and two units upward to triangle $B'I'G'$, in such a way that $B'$ is the image of $B$, $I'$ is the image of $I$, and $G'$ is the image of $...
Level 4
Geometry
Since triangle $B^\prime I^\prime G^\prime$ is translated from triangle $BIG,$ the midpoint of $B^\prime G ^\prime $ is the midpoint of $BG$ translated five units left and two units up. The midpoint of $BG$ is at $\left( \frac{1+5}{2}, \frac{1+1}{2} \right) = (3, 1).$ Thus, the midpoint of $B ^\prime G ^\prime$ is at $...
426
$ABCDEFGH$ shown below is a cube. Find $\sin \angle GAC$. [asy] import three; triple A,B,C,D,EE,F,G,H; A = (0,0,0); B = (1,0,0); C = (1,1,0); D= (0,1,0); EE = (0,0,1); F = B+EE; G = C + EE; H = D + EE; draw(B--C--D); draw(B--A--D,dashed); draw(EE--F--G--H--EE); draw(A--EE,dashed); draw(B--F); draw(C--G...
Level 5
Geometry
We draw right triangle $GAC$ within the cube below: [asy] import three; triple A,B,C,D,EE,F,G,H; A = (0,0,0); B = (1,0,0); C = (1,1,0); D= (0,1,0); EE = (0,0,1); F = B+EE; G = C + EE; H = D + EE; draw(B--C--D); draw(B--A--D,dashed); draw(EE--F--G--H--EE); draw(A--EE,dashed); draw(G--A--C,dashed); draw(B--F); draw(C--G...
587
In triangle $ABC$, $AB = 10$, $BC = 14$, and $CA = 16$. Let $D$ be a point in the interior of $\overline{BC}$. Let points $I_B$ and $I_C$ denote the incenters of triangles $ABD$ and $ACD$, respectively. The circumcircles of triangles $BI_BD$ and $CI_CD$ meet at distinct points $P$ and $D$. The maximum possible area of ...
Level 5
Geometry
First, by the Law of Cosines, we have\[\cos BAC = \frac {16^2 + 10^2 - 14^2}{2\cdot 10 \cdot 16} = \frac {256+100-196}{320} = \frac {1}{2},\]so $\angle BAC = 60^\circ$. Let $O_1$ and $O_2$ be the circumcenters of triangles $BI_BD$ and $CI_CD$, respectively. We first compute\[\angle BO_1D = \angle BO_1I_B + \angle I_BO_...
6,114
A circular cylindrical post with a circumference of 4 feet has a string wrapped around it, spiraling from the bottom of the post to the top of the post. The string evenly loops around the post exactly four full times, starting at the bottom edge and finishing at the top edge. The height of the post is 12 feet. What is ...
Level 5
Geometry
Each time the string spirals around the post, it travels 3 feet up and 4 feet around the post. If we were to unroll this path, it would look like: [asy] size(150); draw((0,0)--(0,3)--(4,3)--(4,0)--cycle, linewidth(.7)); draw((0,0)--(4,3),linewidth(.7)); label("3",(0,1.5),W); label("4",(2,3),N); [/asy] Clearly, a 3-4-5...
502
The isosceles trapezoid shown has side lengths as labeled. How long is segment AC? [asy] unitsize(1.5mm); defaultpen(linewidth(.7pt)+fontsize(10pt)); dotfactor=3; pair A=(0,0), B=(21,0), C=(15,8), D=(6,8); pair[] dots={A,B,C,D}; draw(A--B--C--D--cycle); dot(dots); label("A",A,SW); label("B",B,SE); label("C",C,NE); la...
Level 3
Geometry
Define $E$ and $F$ to be the feet of the perpendiculars drawn to $AB$ from $C$ and $D$ respectively. Since $EF=CD=9$, we find $AF=(21-9)/2=6$ and $AE=AF+FE=15$. Also, from the Pythagorean theorem, $CE=DF=\sqrt{10^2-6^2}=8$. Again using the Pythagorean theorem, $AC=\sqrt{CE^2+AE^2}=\sqrt{8^2+15^2}=\boxed{17}$ units. ...
291
In rectangle $ABCD$, $AB=100$. Let $E$ be the midpoint of $\overline{AD}$. Given that line $AC$ and line $BE$ are perpendicular, find the greatest integer less than $AD$.
Level 5
Geometry
[asy] pair A=(0,10), B=(0,0), C=(14,0), D=(14,10), Q=(0,5); draw (A--B--C--D--cycle); pair E=(7,10); draw (B--E); draw (A--C); pair F=(6.7,6.7); label("\(E\)",E,N); label("\(A\)",A,NW); label("\(B\)",B,SW); label("\(C\)",C,SE); label("\(D\)",D,NE); label("\(F\)",F,W); label("\(100\)",Q,W); [/asy] From the problem, $AB=...
6,118
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?
Level 2
Geometry
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...
26
An octagon is inscribed in a square so that the vertices of the octagon trisect the sides of the square. The perimeter of the square is 108 centimeters. What is the number of square centimeters in the area of the octagon?
Level 4
Geometry
Each side of the square has length $27$. Each trisected segment therefore has length $9$. We can form the octagon by taking away four triangles, each of which has area $\frac{(9)(9)}{2}$, for a total of $(2)(9)(9) = 162$. The total area of the square is $27^2=729$, so the area of the octagon is $729-162=\boxed{567}$.
120
In quadrilateral $ABCD$, $\angle B$ is a right angle, diagonal $\overline{AC}$ is perpendicular to $\overline{CD}$, $AB=18$, $BC=21$, and $CD=14$. Find the perimeter of $ABCD$.
Level 5
Geometry
From the problem statement, we construct the following diagram: [asy] pointpen = black; pathpen = black + linewidth(0.65); pair C=(0,0), D=(0,-14),A=(-(961-196)^.5,0),B=IP(circle(C,21),circle(A,18)); D(MP("A",A,W)--MP("B",B,N)--MP("C",C,E)--MP("D",D,E)--A--C); D(rightanglemark(A,C,D,40)); D(rightanglemark(A,B,C,40)); [...
6,099
A circle with center $O$ has radius $8$ units and circle $P$ has radius $2$ units. The circles are externally tangent to each other at point $Q$. Segment $TS$ is the common external tangent to circle $O$ and circle $P$ at points $T$ and $S$, respectively. What is the length of segment $OS$? Express your answer in s...
Level 5
Geometry
We create a diagram with the given information from the problem: [asy] draw(Circle((0,0),8)); draw(Circle((10,0),2)); dot((0,0));dot((10,0)); label("$O$",(0,0),SW); label("$P$",(10,0),SW); dot((8,0)); label("$Q$",(8,0),SW); label("$T$",(4.6,6.6),NE); label("$S$",(11,1.7),NE); draw((4.6,6.6)--(11,1.7)); [/asy] We dra...
964
In tetrahedron $ABCD$, edge $AB$ has length 3 cm. The area of face $ABC$ is $15\mbox{cm}^2$ and the area of face $ABD$ is $12 \mbox { cm}^2$. These two faces meet each other at a $30^\circ$ angle. Find the volume of the tetrahedron in $\mbox{cm}^3$.
Level 5
Geometry
It is clear that $DX=8$ and $CX=10$ where $X$ is the foot of the perpendicular from $D$ and $C$ to side $AB$. Thus $[DXC]=\frac{ab\sin{c}}{2}=20=5 \cdot h \rightarrow h = 4$ where h is the height of the tetrahedron from $D$. Hence, the volume of the tetrahedron is $\frac{bh}{3}=15\cdot \frac{4}{3}=\boxed{20}$.
6,006
$ABCD$ is a rectangular sheet of paper. $E$ and $F$ are points on $AB$ and $CD$ respectively such that $BE < CF$. If $BCFE$ is folded over $EF$, $C$ maps to $C'$ on $AD$ and $B$ maps to $B'$ such that $\angle{AB'C'} \cong \angle{B'EA}$. If $AB' = 5$ and $BE = 23$, then the area of $ABCD$ can be expressed as $a + b\sqrt...
Level 5
Geometry
Let $\angle{AB'C'} = \theta$. By some angle chasing in $\triangle{AB'E}$, we find that $\angle{EAB'} = 90^{\circ} - 2 \theta$. Before we apply the law of sines, we're going to want to get everything in terms of $\sin \theta$, so note that $\sin \angle{EAB'} = \sin(90^{\circ} - 2 \theta) = \cos 2 \theta = 1 - 2 \sin^2 \...
6,233
A section is cut out of a circular piece of paper having radius four inches, as shown. Points A and B are then glued together to form a right circular cone. What is the circumference of the base of the resulting cone? Express your answer in terms of $\pi$. (The $270^\circ$ sector forms the cone.) [asy]import graph; d...
Level 4
Geometry
The circumference of the whole circle is $2 \pi \cdot 4 = 8 \pi$. Then the circumference of the base of the cone is \[\frac{270^\circ}{360^\circ} \cdot 8 \pi = \boxed{6 \pi}.\]
384
In $\triangle ABC$ lines $CE$ and $AD$ are drawn so that $\dfrac{CD}{DB}=\dfrac{3}{1}$ and $\dfrac{AE}{EB}=\dfrac{3}{2}$. Let $r=\dfrac{CP}{PE}$ where $P$ is the intersection point of $CE$ and $AD$. Then $r$ equals: [asy] size(8cm); pair A = (0, 0), B = (9, 0), C = (3, 6); pair D = (7.5, 1.5), E = (6.5, 0); pair P = in...
Level 5
Geometry
[asy] size(8cm); pair A = (0, 0), B = (9, 0), C = (3, 6); pair D = (7.5, 1.5), E = (6.5, 0); pair P = intersectionpoints(A--D, C--E)[0]; draw(A--B--C--cycle); draw(A--D); draw(C--E); label("$A$", A, SW); label("$B$", B, SE); label("$C$", C, N); label("$D$", D, NE); label("$E$", E, S); label("$P$", P, S); draw(P--B,dott...
6,222
A circle of radius $2$ has center at $(2,0)$. A circle of radius $1$ has center at $(5,0)$. A line is tangent to the two circles at points in the first quadrant. What is the $y$-intercept of the line?
Level 5
Geometry
Let $D$ and $F$ denote the centers of the circles. Let $C$ and $B$ be the points where the $x$-axis and $y$-axis intersect the tangent line, respectively. Let $E$ and $G$ denote the points of tangency as shown. We know that $AD=DE=2$, $DF=3$, and $FG=1$. Let $FC=u$ and $AB=y$. Triangles $FGC$ and $DEC$ are similar, so ...
247
The areas of three of the faces of a right, rectangular prism are $24 \hspace{.6mm} \mathrm{cm}^2$, $32 \hspace{.6mm} \mathrm{cm}^2$, and $48 \hspace{.6mm} \mathrm{cm}^2$. What is the volume of the prism, in cubic centimeters?
Level 2
Geometry
Let the three dimensions of the prism (length, width, and height, although not necessarily in that order) be $x,y,z$ such that $xy = 24$, $xz = 32$, and $yz = 48$. Then the volume of the prism is $xyz$. Multiplying our three equations together and taking the square root of both sides, we find that $xyz = \sqrt{24\cdo...
75
Three congruent isosceles triangles $DAO$, $AOB$ and $OBC$ have $AD=AO=OB=BC=10$ and $AB=DO=OC=12$. These triangles are arranged to form trapezoid $ABCD$, as shown. Point $P$ is on side $AB$ so that $OP$ is perpendicular to $AB$. [asy] pair A, B, C, D, O, P; A= (6, 8); B=(18, 8); C=(24, 0); D=(0,0); O=(12,0); P=(12,...
Level 4
Geometry
Since $\triangle AOB$ is isosceles with $AO=OB$ and $OP$ is perpendicular to $AB$, point $P$ is the midpoint of $AB$, so $AP=PB=\frac{1}{2}AB=\frac{1}{2}(12)=6$. By the Pythagorean Theorem, $OP = \sqrt{AO^2 - AP^2}=\sqrt{10^2-6^2}=\sqrt{64}={8}$. Since $ABCD$ is a trapezoid with height of length 8 ($OP$ is the height...
892
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?
Level 4
Geometry
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...
63
Three circles, each of radius $3$, are drawn with centers at $(14, 92)$, $(17, 76)$, and $(19, 84)$. A line passing through $(17,76)$ is such that the total area of the parts of the three circles to one side of the line is equal to the total area of the parts of the three circles to the other side of it. What is the ab...
Level 5
Geometry
First of all, we can translate everything downwards by $76$ and to the left by $14$. Then, note that a line passing through a given point intersecting a circle with a center as that given point will always cut the circle in half, so we can re-phrase the problem: Two circles, each of radius $3$, are drawn with centers a...
6,005
$ABC$ is a triangle: $A=(0,0), B=(36,15)$ and both the coordinates of $C$ are integers. What is the minimum area $\triangle ABC$ can have? $\textbf{(A)}\ \frac{1}{2} \qquad \textbf{(B)}\ 1 \qquad \textbf{(C)}\ \frac{3}{2} \qquad \textbf{(D)}\ \frac{13}{2}\qquad \textbf{(E)}\ \text{there is no minimum}$
Level 5
Geometry
Let $C$ have coordinates $(p, q)$. Then by the Shoelace Formula, the area of $\triangle ABC$ is $\frac{3}{2} \lvert {12q-5p} \rvert$. Since $p$ and $q$ are integers, $\lvert {12q-5p} \rvert$ is a positive integer, and by Bezout's Lemma, it can equal $1$ (e.g. with $q = 2, p = 5$), so the minimum area is $\frac{3}{2} \t...
6,206
Find the ratio of the area of $\triangle BCX$ to the area of $\triangle ACX$ in the diagram if $CX$ bisects $\angle ACB$. Express your answer as a common fraction. [asy] import markers; real t=27/(27+30); pair A=(-15.57,0); pair B=(8.43,0); pair C=(0,25.65); pair X=t*A+(1-t)*B; draw(C--A--B--C--X); label("$A$",A,SW)...
Level 4
Geometry
The Angle Bisector Theorem tells us that \[\frac{BX}{AX}=\frac{BC}{AC}=\frac{27}{30}=\frac{9}{10}.\]Since $\triangle BCX$ and $\triangle ACX$ share the same height, the ratio of their areas is simply the ratio of their bases, so our answer is \[\frac{BX}{AX}=\boxed{\frac{9}{10}}.\]
496
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.
Level 4
Geometry
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...
409
The diameter $AB$ of a circle of radius $2$ is extended to a point $D$ outside the circle so that $BD=3$. Point $E$ is chosen so that $ED=5$ and line $ED$ is perpendicular to line $AD$. Segment $AE$ intersects the circle at a point $C$ between $A$ and $E$. What is the area of $\triangle ABC$? $\textbf{(A)}\ \frac{120}...
Level 5
Geometry
[asy] /* Geogebra to Asymptote conversion, documentation at artofproblemsolving.com/Wiki, go to User:Azjps/geogebra */ import graph; size(8.865514650638614cm); real labelscalefactor = 0.5; /* changes label-to-point distance */ pen dps = linewidth(0.7) + fontsize(10); defaultpen(dps); /* default pen style */ pen dots...
6,172
A telephone pole is supported by a steel cable which extends from the top of the pole to a point on the ground 3 meters from its base. When Leah walks 2.5 meters from the base of the pole toward the point where the cable is attached to the ground, her head just touches the cable. Leah is 1.5 meters tall. How many meter...
Level 3
Geometry
First, let us draw a diagram (not to scale!): [asy] pair A,B,C,D,E; A=(0,0); B=(0,4.5); C=(6,0); D=(5,0); E=(5,0.75); draw(A--B--C--cycle); draw(D--E); label("A",A,W); label("B",B,W); label("C",C+(0.4,0)); label("D",D, NW); label("E",E+(0.3,0.2)); [/asy] Here, $AB$ is the telephone pole and $C$ is the point in the g...
153
The radius of a sphere is $p$ units and the radius of a hemisphere is $2p$ units. What is the ratio of the volume of the sphere to the volume of the hemisphere?
Level 3
Geometry
The volume of the sphere is \[\frac{4}{3}\pi p^3\] and the volume of the hemisphere is \[\frac{1}{2}\cdot \frac{4}{3}\pi (2p)^3 = \frac{4}{3}\pi p^3 \cdot 4.\] Thus the ratio of the volume of the sphere to the volume of the hemisphere is $\boxed{\frac{1}{4}}$.
1,086
The same amount of steel used to create eight solid steel balls, each with a radius of 1 inch, is used to create one larger steel ball. What is the radius of the larger ball? [asy] size(150); filldraw(circle((0,0),1),gray); filldraw(circle((.9,-.8),1),gray); filldraw(circle((1.8,.9),1),gray); filldraw(circle((2,0),1),...
Level 3
Geometry
The amount of steel used to create one ball with radius 1 is $\frac{4}{3}\pi(1^3)=\frac{4}{3}\pi$; the amount of steel used to create eight of these balls is $8\cdot \frac{4}{3}\pi = \frac{32}{3}\pi$. Let the radius of the large steel be $r$. We have $\frac{4}{3}\pi r^3 = \frac{32}{3}\pi$; solving for $r$ yields $r^3...
457
What is the diameter of the circle inscribed in triangle $ABC$ if $AB = 11,$ $AC=6,$ and $BC=7$? Express your answer in simplest radical form.
Level 4
Geometry
Let $d$ be the diameter of the inscribed circle, and let $r$ be the radius of the inscribed circle. Let $s$ be the semiperimeter of the triangle, that is, $s=\frac{AB+AC+BC}{2}=12$. Let $K$ denote the area of $\triangle ABC$. Heron's formula tells us that \begin{align*} K &= \sqrt{s(s-AB)(s-AC)(s-BC)} \\ &= \sqrt{12\c...
1,099
The vertices of a square are the centers of four circles as shown below. Given each side of the square is 6cm and the radius of each circle is $2\sqrt{3}$cm, find the area in square centimeters of the shaded region. [asy] fill( (-1,-1)-- (1,-1) -- (1,1) -- (-1,1)--cycle, gray); fill( Circle((1,1), 1.2), white); fill( C...
Level 5
Geometry
[asy] fill( (-1,-1)-- (1,-1) -- (1,1) -- (-1,1)--cycle, gray); fill( Circle((1,1), 1.2), white); fill( Circle((-1,-1), 1.2), white); fill( Circle((1,-1),1.2), white); fill( Circle((-1,1), 1.2), white); draw( Arc((1,1),1.2 ,180,270)); draw( Arc((1,-1),1.2,90,180)); draw( Arc((-1,-1),1.2,0,90)); draw( Arc((-1,1),1.2,0,-9...
1,025
In right triangle $ABC$, shown below, $\cos{C}=\frac{9\sqrt{130}}{130}$. Find $AC$. [asy] draw((0,0)--(7,0)--(0,9)--cycle,black+linewidth(1)); draw(rightanglemark((7,0),(0,0),(0,9),20),black+linewidth(1)); label("$A$",(0,0),W); label("$B$",(7,0),E); label("$C$",(0,9),W); label("$\sqrt{130}$",(7,0)--(0,9),NE); [/asy]
Level 2
Geometry
Since $\cos{C}=\frac{9\sqrt{130}}{130}$ and $\cos{C}=\frac{AC}{BC}$, we have $\frac{AC}{BC}=\frac{AC}{\sqrt{130}}=\frac{9\sqrt{130}}{130}$. This means that $AC=\frac{9\sqrt{130}}{130}\cdot\sqrt{130}=\frac{9\cdot\sqrt{130}\cdot\sqrt{130}}{130}=\boxed{9}$.
184
When a right triangle is rotated about one leg, the volume of the cone produced is $800\pi \;\textrm{ cm}^3$. When the triangle is rotated about the other leg, the volume of the cone produced is $1920\pi \;\textrm{ cm}^3$. What is the length (in cm) of the hypotenuse of the triangle?
Level 5
Geometry
Let one leg of the triangle have length $a$ and let the other leg have length $b$. When we rotate around the leg of length $a$, the result is a cone of height $a$ and radius $b$, and so of volume $\frac 13 \pi ab^2 = 800\pi$. Likewise, when we rotate around the leg of length $b$ we get a cone of height $b$ and radius $...
6,008
What is the area, in square units, of a trapezoid bounded by the lines $y = x$, $y = 10$, $y = 5$ and the $y$-axis? Express your answer as a decimal to the nearest tenth.
Level 3
Geometry
The vertices of the trapezoid are $(5,5)$, $(10,10)$, $(0,10)$, and $(0,5)$. Its bases are $5$ and $10$ units long, and its height is $5$ units. Averaging the bases and multiplying by the height, we find an area of $\left(\frac{5+10}{2}\right)(5)=\boxed{37.5}$ square units. [asy] unitsize(2mm); defaultpen(linewidth(...
715
Consider the set of points that are inside or within one unit of a rectangular parallelepiped (box) that measures 3 by 4 by 5 units. Given that the volume of this set is $\displaystyle {{m+n\pi}\over p}$, where $m$, $n$, and $p$ are positive integers, and $n$ and $p$ are relatively prime, find $m+n+p$.
Level 5
Geometry
First consider the points in the six parallelepipeds projecting 1 unit outward from the original parallelepiped. Two of these six parallelepipeds are 1 by 3 by 4, two are 1 by 3 by 5, and two are 1 by 4 by 5. The sum of their volumes is $2(1\cdot3\cdot4+1\cdot3\cdot5+1\cdot4\cdot5)=94$. Next consider the points in the ...
25,000
In rectangle $ADEH$, points $B$ and $C$ trisect $\overline{AD}$, and points $G$ and $F$ trisect $\overline{HE}$. In addition, $AH=AC=2$. What is the area of quadrilateral $WXYZ$ shown in the figure? [asy] unitsize(1cm); pair A,B,C,D,I,F,G,H,U,Z,Y,X; A=(0,0); B=(1,0); C=(2,0); D=(3,0); I=(3,2); F=(2,2); G=(1,2); H...
Level 4
Geometry
First note that since points $B$ and $C$ trisect $\overline{AD}$, and points $G$ and $F$ trisect $\overline{HE}$, we have $HG = GF = FE = AB = BC = CD = 1$. Also, $\overline{HG}$ is parallel to $\overline{CD}$ and $HG = CD$, so $CDGH$ is a parallelogram. Similarly, $\overline{AB}$ is parallel to $\overline{FE}$ an...
240
A pipe with inside diameter 10'' is to carry water from a reservoir to a small town in an arid land. Neglecting the friction and turbulence of the water against the inside of the pipes, what is the minimum number of 2''-inside-diameter pipes of the same length needed to carry the same volume of water to the arid town?
Level 4
Geometry
Let the length of the pipes be $h$. The volume of the 10-inch pipe is $\pi (5^2) (h) = 25\pi h$ cubic inches and the volume of each 2-inch pipe is $\pi (1^2)(h) = \pi h$ cubic inches. Hence we see it takes exactly 25 2-inch pipes to match the volume of one 10-inch pipe. The answer is $\boxed{25}$ pipes.
651
The surface area of a sphere with radius $r$ is $4\pi r^2$. Including the area of its circular base, what is the total surface area of a hemisphere with radius 6 cm? Express your answer in terms of $\pi$. [asy] import markers; size(150); import geometry; draw((0,-7)--(0,-1),Arrow); draw((10,10)--(5,5),Arrow); label("...
Level 3
Geometry
The base of the hemisphere is a circle with radius 6 and area $6^2\pi=36\pi$. The curved top of the hemisphere has half the surface area of a full sphere, which has surface area $4\pi(6^2)=144\pi$, so the curved top of the hemisphere has $144\pi/2=72\pi$. The total surface area of the hemisphere is $36\pi+72\pi=\boxe...
399
A rectangular box $P$ is inscribed in a sphere of radius $r$. The surface area of $P$ is 384, and the sum of the lengths of its 12 edges is 112. What is $r$?
Level 5
Geometry
Let the dimensions of $P$ be $x$, $y$, and $z$. The sum of the lengths of the edges of $P$ is $4(x+y+z)$, and the surface area of $P$ is $2xy+2yz+2xz$, so \[ x+y+z=28 \quad\text{and}\quad 2xy+2yz+2xz=384. \] Each internal diagonal of $P$ is a diameter of the sphere, so \begin{align*} (2r)^2&=(x^2+y^2+z^2)\\ &=(x+y+z)^2...
191
Tetrahedron $ABCD$ has $AD=BC=28$, $AC=BD=44$, and $AB=CD=52$. For any point $X$ in space, suppose $f(X)=AX+BX+CX+DX$. The least possible value of $f(X)$ can be expressed as $m\sqrt{n}$, where $m$ and $n$ are positive integers, and $n$ is not divisible by the square of any prime. Find $m+n$.
Level 5
Geometry
Let $M$ and $N$ be midpoints of $\overline{AB}$ and $\overline{CD}$. The given conditions imply that $\triangle ABD\cong\triangle BAC$ and $\triangle CDA\cong\triangle DCB$, and therefore $MC=MD$ and $NA=NB$. It follows that $M$ and $N$ both lie on the common perpendicular bisector of $\overline{AB}$ and $\overline{CD}...
6,149
A solid right prism $ABCDEF$ has a height of 16, as shown. Also, its bases are equilateral triangles with side length 12. Points $X$, $Y$, and $Z$ are the midpoints of edges $AC$, $BC$, and $DC$, respectively. Determine the perimeter of triangle $XYZ$. [asy] pair A, B, C, D, E, F, X, Y, Z; A=(0,0); B=(12,0); C=(6,-6); ...
Level 3
Geometry
Since $\triangle ABC$ is equilateral with side length 12 and $X$ and $Y$ are the midpoints of $CA$ and $CB$ respectively, we have $CX=CY=\frac{1}{2}(12)=6$. Since the height of the prism is 16 and $Z$ is the midpoint of $CD$ we have $CZ = \frac{1}{2}(16)=8$. We have $\angle ACD = \angle BCD = 90^\circ$ since faces $A...
180
Let $ABCD$ and $BCFG$ be two faces of a cube with $AB=12$. A beam of light emanates from vertex $A$ and reflects off face $BCFG$ at point $P$, which is 7 units from $\overline{BG}$ and 5 units from $\overline{BC}$. The beam continues to be reflected off the faces of the cube. The length of the light path from the time ...
Level 5
Geometry
When a light beam reflects off a surface, the path is like that of a ball bouncing. Picture that, and also imagine X, Y, and Z coordinates for the cube vertices. The coordinates will all involve 0's and 12's only, so that means that the X, Y, and Z distance traveled by the light must all be divisible by 12. Since the l...
6,068
What is the area, in square units, of triangle $ABC$? [asy] unitsize(0.15inch); path X = (-6.5, 0)--(5.5, 0); path Y = (0, -3.5)--(0, 7.5); draw(X); draw(Y); for(int n=-6; n <= 5; ++n) if( n != 0 ) draw( (n,0.25)--(n,-0.25) ); for(int n=-3; n <= 7; ++n) if( n != 0 ) draw( (0.25,n)--(-0.25,n) ); pair A = (-4,3); pair ...
Level 4
Geometry
Define points $D$ $E$ and $F$ as shown. The area of rectangle $CDEF$ is the sum of the areas of the four triangles $BEA$, $BFC$, $CDA$, and $ABC$. The areas of the first three triangles may be found directly using the area formula $\frac{1}{2}$(base)(height). The area of triangle $ABC$ is the area of the rectangle m...
718
Compute $\cos 0^\circ$.
Level 1
Geometry
Rotating the point $(1,0)$ about the origin by $0^\circ$ counterclockwise gives us the point $(1,0)$, so $\cos 0^\circ = \boxed{1}$.
450
Compute $\sin 45^\circ$.
Level 2
Geometry
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...
286
In $\triangle{ABC}, AB=10, \angle{A}=30^\circ$ , and $\angle{C=45^\circ}$. Let $H, D,$ and $M$ be points on the line $BC$ such that $AH\perp{BC}$, $\angle{BAD}=\angle{CAD}$, and $BM=CM$. Point $N$ is the midpoint of the segment $HM$, and point $P$ is on ray $AD$ such that $PN\perp{BC}$. Then $AP^2=\dfrac{m}{n}$, where ...
Level 5
Geometry
[asy] unitsize(20); pair A = MP("A",(-5sqrt(3),0)), B = MP("B",(0,5),N), C = MP("C",(5,0)), M = D(MP("M",0.5(B+C),NE)), D = MP("D",IP(L(A,incenter(A,B,C),0,2),B--C),N), H = MP("H",foot(A,B,C),N), N = MP("N",0.5(H+M),NE), P = MP("P",IP(A--D,L(N,N-(1,1),0,10))); D(A--B--C--cycle); D(B--H--A,blue+dashed); D(A--D); D(P--N)...
6,139
In the diagram, $\triangle ABE$, $\triangle BCE$ and $\triangle CDE$ are right-angled, with $\angle AEB=\angle BEC = \angle CED = 60^\circ$, and $AE=24$. [asy] pair A, B, C, D, E; A=(0,20.785); B=(0,0); C=(9,-5.196); D=(13.5,-2.598); E=(12,0); draw(A--B--C--D--E--A); draw(B--E); draw(C--E); label("A", A, N); label("B",...
Level 3
Geometry
Recognizing that all our triangles in the diagram are 30-60-90 triangles, we recall that the ratio of the longer leg to the hypotenuse in such a triangle is $\frac{\sqrt{3}}{2}$. Therefore, we can see that: \begin{align*} AB & = 24 \left(\frac{\sqrt{3}}{2}\right) = 12\sqrt{3}\\ BC & = 12 \left(\frac{\sqrt{3}}{2}\right)...
791
In triangle $ABC,$ $AB = 13,$ $BC = 14,$ $AC = 15,$ and point $G$ is the intersection of the medians. Points $A',$ $B',$ and $C',$ are the images of $A,$ $B,$ and $C,$ respectively, after a $180^\circ$ rotation about $G.$ What is the area of the union of the two regions enclosed by the triangles $ABC$ and $A'B'C'?$
Level 5
Geometry
Since a $13-14-15$ triangle is a $5-12-13$ triangle and a $9-12-15$ triangle "glued" together on the $12$ side, $[ABC]=\frac{1}{2}\cdot12\cdot14=84$. There are six points of intersection between $\Delta ABC$ and $\Delta A'B'C'$. Connect each of these points to $G$. [asy] size(8cm); pair A,B,C,G,D,E,F,A_1,A_2,B_1,B_2,C_...
6,081
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...
Level 5
Geometry
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...
960
Let triangle $ABC$ be a right triangle in the xy-plane with a right angle at $C$. Given that the length of the hypotenuse $AB$ is $60$, and that the medians through $A$ and $B$ lie along the lines $y=x+3$ and $y=2x+4$ respectively, find the area of triangle $ABC$.
Level 5
Geometry
Translate so the medians are $y = x$, and $y = 2x$, then model the points $A: (a,a)$ and $B: (b,2b)$. $(0,0)$ is the centroid, and is the average of the vertices, so $C: (- a - b, - a - 2b)$ $AB = 60$ so $3600 = (a - b)^2 + (2b - a)^2$ $3600 = 2a^2 + 5b^2 - 6ab \ \ \ \ (1)$ $AC$ and $BC$ are perpendicular, so the produ...
6,010
What is the area of the shaded region in the figure below? Round your answer to the nearest square centimeter. [asy] draw((0,0) -- (3,0) -- (3,3) -- (0,3)--cycle) ; draw((3,0)-- (12,0) -- (12,9) -- (3, 9)--cycle); label ( "3 cm", (0,1.5), W); label ( "3 cm", (1.5 ,0), S); label ( "9 cm", (3+9/2 ,0), S);label ( "9 cm"...
Level 4
Geometry
Label points $O,A,B,C,D,E$ as follows. [asy] draw((0,0) -- (3,0) -- (3,3) -- (0,3)--cycle) ; draw((3,0)-- (12,0) -- (12,9) -- (3, 9)--cycle); label ( "3", (0,1.5), W); label ( "3", (1.5 ,0), S); label ( "9", (3+9/2 ,0), S);label ( "9", (12 ,9/2), E); draw( (0,0) -- (12, 9)); fill( (3, 9/4) -- (12, 9) -- (3,9)-- cycle...
124
One of the five faces of the triangular prism shown here will be used as the base of a new pyramid. The numbers of exterior faces, vertices and edges of the resulting shape (the fusion of the prism and pyramid) are added. What is the maximum value of this sum? [asy] draw((0,0)--(9,12)--(25,0)--cycle); draw((9,12)--(12...
Level 5
Geometry
The original prism has 5 faces, 9 edges, and 6 vertices. If the new pyramid is added to a triangular face, it will cover one of these faces while adding 1 new vertex, 3 new edges, and 3 new faces. If instead the new pyramid is added to a quadrilateral face, it will cover one of these faces while adding 1 new vertex, ...
758
In the figure shown, arc $ADB$ and arc $BEC$ are semicircles, each with a radius of one unit. Point $D$, point $E$ and point $F$ are the midpoints of arc $ADB$, arc $BEC$ and arc $DFE$, respectively. If arc $DFE$ is also a semicircle, what is the area of the shaded region? [asy] unitsize(0.5inch); path t=(1,1)..(2,0)-...
Level 4
Geometry
Mark segments $BF$ and $DE$ and label their intersection $P$. Now, slide sector $FPE$ on to sector $DB$ and slide sector $FPD$ on to sector $EB$. The shaded region is now a rectangle with side lengths $1$ and $2$, thus the area of the shaded region is $\boxed{2}$.
799
Circle $C$ with radius 2 has diameter $\overline{AB}$. Circle D is internally tangent to circle $C$ at $A$. Circle $E$ is internally tangent to circle $C$, externally tangent to circle $D$, and tangent to $\overline{AB}$. The radius of circle $D$ is three times the radius of circle $E$, and can be written in the form $...
Level 5
Geometry
[asy] import graph; size(7.99cm); real labelscalefactor = 0.5; pen dps = linewidth(0.7) + fontsize(10); defaultpen(dps); pen dotstyle = black; real xmin = 4.087153740193288, xmax = 11.08175859031552, ymin = -4.938019122704778, ymax = 1.194137062512079; draw(circle((7.780000000000009,-1.320000000000002), 2.000000000...
6,140
In the diagram, four circles of radius 4 units intersect at the origin. What is the number of square units in the area of the shaded region? Express your answer in terms of $\pi$. [asy] import olympiad; import geometry; size(100); defaultpen(linewidth(0.8)); fill(Arc((1,0),1,90,180)--Arc((0,1),1,270,360)--cycle,gray(0....
Level 4
Geometry
The shaded region consists of 8 copies of the checkered region in the figure below. The area of this region is the difference between the area of a quarter-circle and the area of an isosceles right triangle. The area of the quarter-circle is $\frac{1}{4}\pi (4)^2=4\pi$ square units, and the area of the isosceles righ...
648
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("$T$"...
Level 3
Geometry
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(...
909
$A$, $B$, $C$, and $D$ are points on a circle, and segments $\overline{AC}$ and $\overline{BD}$ intersect at $P$, such that $AP=8$, $PC=1$, and $BD=6$. Find $BP$, given that $BP < DP.$ [asy] unitsize(0.6 inch); draw(circle((0,0),1)); draw((-0.3,0.94)--(0.3,-0.94)); draw((-0.7,-0.7)--(0.7,-0.7)); label("$A$",(-0.3,0...
Level 3
Geometry
Writing $BP=x$ and $PD=6-x$, we have that $BP < 3$. Power of a point at $P$ gives $AP \cdot PC = BP \cdot PD$ or $8=x(6-x)$. This can be solved for $x=2$ and $x=4$, and we discard the latter, leaving $BP = \boxed{2}$.
111
A circle is circumscribed about an equilateral triangle with side lengths of $9$ units each. What is the area of the circle, in square units? Express your answer in terms of $\pi$.
Level 4
Geometry
[asy] size(100); defaultpen(linewidth(.8)); draw((0,0)--(4.5,7.794)--(9,0)--cycle); draw(Circle((4.5,2.598),5.196)); draw((4.5,7.794)--(4.5,0)); dot((4.5,2.598)); label("$O$",(4.5,2.598),W); label("$A$",(4.5,7.794),N); label("$B$",(9,0),E); label("$M$",(4.5,0),S); [/asy] Above is the diagram implied by the problem, wi...
655
A unit cube is cut twice to form three triangular prisms, two of which are congruent, as shown in Figure 1. The cube is then cut in the same manner along the dashed lines shown in Figure 2. This creates nine pieces. What is the volume of the piece that contains vertex $W$? [asy] path a=(0,0)--(10,0)--(10,10)--(0,10)--...
Level 5
Geometry
The piece that contains $W$ is shown. It is a pyramid with vertices $V, W, X,Y$, and $Z$. Its base $WXYZ$ is a square with sides of length $1/2$ and its altitude $VW$ is 1. Hence the volume of this pyramid is \[ \frac{1}{3}\left(\frac{1}{2}\right)^2(1)=\boxed{\frac{1}{12}}. \][asy] unitsize(0.3cm); draw((0,0)--(10,0)-...
870
A sphere is inscribed in a cube with edge length 9 inches. Then a smaller cube is inscribed in the sphere. How many cubic inches are in the volume of the inscribed cube? Express your answer in simplest radical form.
Level 5
Geometry
We draw a diagram: [asy] size(140); 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)); dot((6,6)); 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),...
604
Let $ABCDEF$ be a regular hexagon. Let $G$, $H$, $I$, $J$, $K$, and $L$ be the midpoints of sides $AB$, $BC$, $CD$, $DE$, $EF$, and $AF$, respectively. The segments $\overline{AH}$, $\overline{BI}$, $\overline{CJ}$, $\overline{DK}$, $\overline{EL}$, and $\overline{FG}$ bound a smaller regular hexagon. Let the ratio of ...
Level 5
Geometry
[asy] defaultpen(0.8pt+fontsize(12pt)); pair A,B,C,D,E,F; pair G,H,I,J,K,L; A=dir(0); B=dir(60); C=dir(120); D=dir(180); E=dir(240); F=dir(300); draw(A--B--C--D--E--F--cycle,blue); G=(A+B)/2; H=(B+C)/2; I=(C+D)/2; J=(D+E)/2; K=(E+F)/2; L=(F+A)/2; int i; for (i=0; i<6; i+=1) { draw(rotate(60*i)*(A--H),dotted); } p...
6,125
The lengths of two sides of a triangle are 33 units and 42 units. The third side also has an integral length. What is the least possible number of units in the perimeter of the triangle?
Level 3
Geometry
The sum of the smaller two sides must exceed the greatest side, so if $x$ is the missing side then $x+33>42\implies x>9$. The smallest integer greater than 9 is 10, so the least perimeter is $10+33+42=\boxed{85}$ units.
337
The perimeter of triangle $APM$ is $152$, and the angle $PAM$ is a right angle. A circle of radius $19$ with center $O$ on $\overline{AP}$ is drawn so that it is tangent to $\overline{AM}$ and $\overline{PM}$. Given that $OP=m/n$ where $m$ and $n$ are relatively prime positive integers, find $m+n$.
Level 5
Geometry
Let the circle intersect $\overline{PM}$ at $B$. Then note $\triangle OPB$ and $\triangle MPA$ are similar. Also note that $AM = BM$ by power of a point. Using the fact that the ratio of corresponding sides in similar triangles is equal to the ratio of their perimeters, we have\[\frac{19}{AM} = \frac{152-2AM-19+19}{152...
6,070
A cone is inverted and filled with water to 3/4 of its height. What percent of the cone's volume is filled with water? Express your answer as a decimal to the nearest ten-thousandth. (You should enter 10.0000 for $10\%$ instead of 0.1000.)
Level 5
Geometry
Let the cone have height $h$ and radius $r$, so its volume is \[\frac{1}{3}\pi r^2h.\]When the cone is filled with water, the amount of water in the cone forms a smaller cone that is similar to the original cone. This smaller cone has height $\frac{3}{4}h$, and by similar triangles, radius $\frac{3}{4}r$. So, the sma...
725
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...
Level 5
Geometry
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_...
6,083
In $\triangle XYZ$, we have $\angle X = 90^\circ$ and $\tan Y = \frac34$. If $YZ = 30$, then what is $XY$?
Level 3
Geometry
[asy] pair X,Y,Z; X = (0,0); Y = (16,0); Z = (0,12); draw(X--Y--Z--X); draw(rightanglemark(Y,X,Z,23)); label("$X$",X,SW); label("$Y$",Y,SE); label("$Z$",Z,N); label("$30$",(Y+Z)/2,NE); label("$3k$",(Z)/2,W); label("$4k$",Y/2,S); [/asy] Since $\triangle XYZ$ is a right triangle with $\angle X = 90^\circ$, ...
560
The volume of a cylinder is $54\pi$ $\text{cm}^3$. How many cubic centimeters are in the volume of a cone with the same radius and height as the cylinder? Express your answer in terms of $\pi$. [asy] import solids; currentprojection=orthographic(0,100,25); defaultpen(linewidth(0.8)); revolution cyl = cylinder((5,0,0),1...
Level 2
Geometry
A cone with radius $r$ and height $h$ has volume $(1/3)\pi r^2 h$; a cylinder with the same radius and height has volume $\pi r^2 h$. Thus we see the volume of the corresponding cone has 1/3 the volume of the cylinder, which is $(1/3)(54\pi = \boxed{18\pi}$ cubic cm.
211
A bottled water company has designed a new cup for its dispenser. The cup will be a right circular cone with a three-inch radius. How tall will the cup need to be to hold 93 cubic inches of water? Express your answer to the nearest whole number.
Level 4
Geometry
The volume of a cone with radius $r$ and height $h$ is \[\frac{1}{3} \pi r^2 h.\] Therefore, we want $h$ to satisfy \[\frac{1}{3} \pi \cdot 3^2 \cdot h \ge 93,\] or \[h \ge \frac{93}{3 \pi} \approx 9.87.\] Therefore, the height must be $\boxed{10}$ inches.
343
Triangle $ABC$ has $\angle C = 60^{\circ}$ and $BC = 4$. Point $D$ is the midpoint of $BC$. What is the largest possible value of $\tan{\angle BAD}$? $\mathrm{(A)}\ \frac{\sqrt{3}}{6}\qquad\mathrm{(B)}\ \frac{\sqrt{3}}{3}\qquad\mathrm{(C)}\ \frac{\sqrt{3}}{2\sqrt{2}}\qquad\mathrm{(D)}\ \frac{\sqrt{3}}{4\sqrt{2}-3}\qqua...
Level 5
Geometry
[asy]unitsize(12mm); pair C=(0,0), B=(4 * dir(60)), A = (8,0), D=(2 * dir(60)); pair E=(1,0), F=(2,0); draw(C--B--A--C); draw(A--D);draw(D--E);draw(B--F); dot(A);dot(B);dot(C);dot(D);dot(E);dot(F); label("\(C\)",C,SW); label("\(B\)",B,N); label("\(A\)",A,SE); label("\(D\)",D,NW); label("\(E\)",E,S); label("\(F\)",F,S);...
6,181
The diagonal of a particular square is 5 inches. The diameter of a particular circle is also 5 inches. By how many square inches is the area of the circle greater than the area of square? Express your answer as a decimal to the nearest tenth. [asy] draw((0,0)--(2,0)--(2,2)--(0,2)--cycle); draw((2,0)--(0,2)); draw(c...
Level 3
Geometry
Let the side length of the square be $s$, so the area of the square is $s^2$. [asy] size(75); draw((0,0)--(2,0)--(2,2)--(0,2)--cycle); draw((2,0)--(0,2)); label("$s$",(1,0),S); label("$s$",(0,1),W); label("$5$",(1,1),NE); [/asy] By the Pythagorean Theorem, we have $s^2+s^2=5^2$, so $2s^2=25$ and $s^2=\frac{25}{2}$, so...
824
$ABCDEFGH$ shown below is a cube with volume 1. Find the volume of pyramid $ABCH$. [asy] import three; triple A,B,C,D,EE,F,G,H; A = (0,0,0); B = (1,0,0); C = (1,1,0); D= (0,1,0); EE = (0,0,1); F = B+EE; G = C + EE; H = D + EE; draw(B--C--D); draw(B--A--D,dashed); draw(EE--F--G--H--EE); draw(A--EE,dashed); draw(B--F);...
Level 4
Geometry
We add the edges of the pyramid to our diagram below. [asy] import three; triple A,B,C,D,EE,F,G,H; A = (0,0,0); B = (1,0,0); C = (1,1,0); D= (0,1,0); EE = (0,0,1); F = B+EE; G = C + EE; H = D + EE; draw(B--C--D); draw(B--A--D,dashed); draw(EE--F--G--H--EE); draw(B--H--A--EE,dashed); draw(A--C,dashed); draw(B--F); draw...
657
[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 $10$. ...
Level 5
Geometry
[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...
6,189
Pyramid $OABCD$ has square base $ABCD,$ congruent edges $\overline{OA}, \overline{OB}, \overline{OC},$ and $\overline{OD},$ and $\angle AOB=45^\circ.$ Let $\theta$ be the measure of the dihedral angle formed by faces $OAB$ and $OBC.$ Given that $\cos \theta=m+\sqrt{n},$ where $m$ and $n$ are integers, find $m+n.$
Level 5
Geometry
[asy] import three; // calculate intersection of line and plane // p = point on line // d = direction of line // q = point in plane // n = normal to plane triple lineintersectplan(triple p, triple d, triple q, triple n) { return (p + dot(n,q - p)/dot(n,d)*d); } // projection of point A onto line BC triple projection...
6,033
In $\triangle ABC$ points $D$ and $E$ lie on $\overline{BC}$ and $\overline{AC}$, respectively. If $\overline{AD}$ and $\overline{BE}$ intersect at $T$ so that $AT/DT=3$ and $BT/ET=4$, what is $CD/BD$? [asy] pair A,B,C,D,I,T; A=(0,0); B=(6,8); C=(11,0); D=(9.33,2.66); I=(7.5,0); T=(6.5,2); label("$T$",T,NW); label("$...
Level 5
Geometry
Let $F$ be a point on $\overline{AC}$ such that $\overline{DF}$ is parallel to $\overline{BE}$. Let $BT = 4x$ and $ET=x$. [asy] pair A,B,C,D,I,T,F; A=(0,0); B=(6,8); C=(11,0); D=(9.33,2.66); I=(7.5,0); T=(6.5,2); F=(9.9,0); draw(D--F,linewidth(0.7)); label("$4x$",(6.5,5.67),W); label("$x$",(7.35,0.8),W); label("$F$",F...
844
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)--(...
Level 2
Geometry
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...
1,019
What is the area, in square units, of triangle $ABC$? [asy] unitsize(1.5mm); defaultpen(linewidth(.7pt)+fontsize(8pt)); dotfactor=4; pair A=(-3,1), B=(7,1), C=(5,-3); pair[] dots={A,B,C}; real[] xticks={-4,-3,-2,-1,1,2,3,4,5,6,7,8}; real[] yticks={3,2,1,-1,-2,-3,-4,-5,-6,-7}; draw(A--B--C--cycle); dot(dots); label("...
Level 2
Geometry
Use the area formula $\frac{1}{2}(\text{base})(\text{height})$ with $AB$ as the base to find the area of triangle $ABC$. We find $AB=7-(-3)=10$ by subtracting the $x$-coordinates of $A$ and $B$. Let $D$ be the foot of the perpendicular line drawn from $C$ to line $AB$. We find a height of $CD=1-(-3)=4$ by subtractin...
822
Let $\triangle XOY$ be a right-angled triangle with $m\angle XOY = 90^{\circ}$. Let $M$ and $N$ be the midpoints of legs $OX$ and $OY$, respectively. Given that $XN=19$ and $YM=22$, find $XY$.
Level 4
Geometry
Let $OM = a$ and $ON = b$. Then $$ 19^2 = (2a)^2 + b^2 \quad \text{and} \quad 22^2 = a^2 + (2b)^2. $$ [asy] unitsize(0.3cm); pair X,Y,O,N,M; X=(0,8); O=(0,0); Y=(13,0); N=(6,0); M=(0,4); path a=X--Y--O--cycle; path b=M--Y; draw(a); draw(X--N); draw(shift((16,0))*a); draw(shift((16,0))*b); for (int i=0; i<2; ++i) { labe...
1,048