A top can fill a cistern in 8 hours and another can empty it in 16 hours. If both the taps are opened simultaneously the time (in hours) to fill the tank is

A. 8
B. 10
C. 16
D. 24

Explanation:

Part filled by insert in 1 hour = 1/8

Part emptied by outlet in 1 hour = 1/16

Net filling in 1 hour = (1/8 – 1/16) = 1/16

Time taken to fill the tank = 1/16 hour= 16 hours