An inlet pipe can fill a tank in 8 minutes. A drain can empty the tank in 10 minutes. If the tank is empty and both the pipe and drain are open, how long will it take before the tank overflows?
A)38 minutes
B)20 minutes
C)2 minutes
D)50 minutes
E)40 minutes

Question

Quizplus · Accepted Answer

The inlet pipe fills the tank at a rate of 1/8 of the tank per minute, and the drain empties it at a rate of 1/10 of the tank per minute. When both are open, the net rate of filling the tank is 1/8 - 1/10 = 1/40 of the tank per minute. Therefore, it will take 40 minutes to fill the tank.

An Inlet Pipe Can Fill a Tank in 8 Minutes