The task is to generate the correct answer for a given math problem.

Example Input: Problem: by selling an article for $ 225 a person gains $ 75 . what is the gain % ?
Example Output: 50 %

Example Input: Problem: two pipes can fill the cistern in 10 hr and 12 hr respectively , while the third empty it in 30 hr . if all pipes are opened simultaneously , then the cistern will be filled in
Example Output: 6.67 hr

Example Input: Problem: there are two positive numbers in the ratio 4 : 8 . if the larger number exceeds the smaller by 16 , then find the smaller number ?
Example Output:
20