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

[EX Q]: 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
[EX A]: 5 / 12

[EX Q]: Problem: the ratio of three numbers is 2 : 3 : 4 and their sum is 180 . the second number of the three numbers is ?
[EX A]: 60

[EX Q]: Problem: the average marks of a class of 35 students is 40 and that of another class of 45 students is 60 . find the average marks of all the students ?
[EX A]:
51.2