instruction:
The task is to generate the correct answer for a given math problem.
question:
Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 7 days , then the fraction of the work that is left is
answer:
11 / 6


question:
Problem: a cycle is bought for rs . 900 and sold for rs . 1170 , find the gain percent ?
answer:
30 %


question:
Problem: the total age of a and b is 12 year more than the total age of b and c . c is how many years younger than a ?
answer:

12