A can do a piece of work n 7 days of 9 hours each and B alone can do it in 6 days of 7 hours each. How long will they take to do it working together 8 2/5 hours a day?

Detailed Solution:

A can complete the work in (7*9) = 63 days B can complete the work in (6*7) = 42 days --> A’s one hour’s work = 1/63 and B’s one hour work = 1/42. (A+B)’s one hour work = 1/63+1/42 = 5/126 Therefore, Both can finish the work in 126/5 hours. Number of days of 8 2/5 hours each = (126*5/(5*42)) = 3 days