A and B can complete a work in 10 and 15 days respectively. A and B start working together and after 4 days, A left the work. Find in how many days work will be completed.

9

Total work = Efficiency × Number of days

Work done by ( A + B ) in 4 days = 5 x 4 = 20

Remaining work = 30 - 20 = 10

Time taken by B to complete the remaining work = \(\frac{10}{2}\)

= 5

Total time taken in doing whole work = 4 + 5 = 9 days