instruction:
The task is to generate the correct answer for a given math problem.
question:
Problem: a work as fast as b . if b can complete a work in 8 days independently , the number of days in which a and b can together finish the work in ?
answer:
2 2 / 3 days


question:
Problem: a can do a work in 15 days and b in 20 days . if they work on it together for 5 days , then the fraction of the work that is left is
answer:
5 / 12


question:
Problem: a group of hikers is planning a trip that will take them up a mountain using one route and back down using another route . they plan to travel down the mountain at a rate of one and a half times the rate they will use on the way up , but the time each route will take is the same . if they will go up the mountain at a rate of 6 miles per day and it will take them two days , how many miles long is the route down the mountain ?
answer:

18