A tank has two pipes, one can fill it with water in 14 hours and the other can empty it in 8 hours. In how many hours will the tank be emptied if both the pipes are opened together when 1/4th of the tank is already filled with water?
Show answer & explanation
Correct answer: D
Explanation
Given:
The first pipe fills the tank in 14 hours
The second pipe empties the tank in 8 hours
The tank is already 1/4 full
Filling rate = 1/14
Emptying rate = −1/8
Combined rate = 1/14 − 1/8 = −3/56
That is, 3/56 of the tank is emptied every hour
Part of the tank emptied = 1/4
Time = (1/4) ÷ (3/56) = 4 hours 40 minutes