Update readme

README.md

@@ -4,10 +4,12 @@ task_categories:
 - text-generation
 ---
 
-This dataset is aimed to teach LLM how to solve basic arithmetic problems.
+This dataset is designed to teach LLM how to solve basic arithmetic problems.
 
 Each row consists of four fields: 
 * `problem` - Problem itself
 * `answer` - Answer to the problem
 * `type` - Type of numbers in the problem
-* `range` - Range of numbers (-N...N) used in the problem
+* `range` - Range of numbers (-N...N) used in the problem
+
+If problem contains an error (e.g. division by zero), `answer` equals "error".