11 Pump A can empty a pool in 4 hours Pump B can empty the s

11. Pump A can empty a pool in 4 hours. Pump B can empty the same pool in 12 hours. If both pumps are working together, which of the following is the amount of time it will take them to empty the pool?

A. 3 hours

B. 4 hours

C. 8 hours

D. 2 hours

Solution

Pump A work in one hour is 1/4 .

PumpB work in one hour is 1/12.

If both work together ,then their work in one hour is 1/4 + 1/12 = 1/3.

So to empty the tank they will take 3 hours..