Question

A pump can fill a tank in 4 hours. Another pump can fill the same tank in 3 hours, and a third pump can fill it in 4 hours. How long would it take to fill the tank with all pumps working?

Answer 1

First pump can fill the tank in 4 hours. So, In 1 hour it fill 1/4 of the tank.

Second pump 1/3

Third one, 1/4

If three pumps are used at the same time, then in 1 hour they will fill

1/4 + 1/3 + 1/4 = 5/6

Therefore tank will be full = 1 ÷ 5/6 = 1.2 hours or 1 hour and 12 minutes