A can do a work in 10 days and B can do the same work in 15 days. If they start working together but stop working after four days, find the fraction of the work that is left.

Question: A can do a work in 10 days and B can do the same work in 15 days. If they start working together but stop working after four days, find the fraction of the work that is left.

Solution:
A's one day work = 1/10
B's one day work = 1/15

(A + B)'s one day work = 1/10 + 1/15 = (3 + 2)/30 = 5/30 = 1/6
A and B's four day work = (1/6) × 4 = 2/3

Therefore,the remaining work = 1 - 2/3 = (3 - 2)/3 = 1/3