Pipe P can fill a tank in 12 hours, and pipe Q can empty the same tank in 18 hours. If both pipes are opened simultaneously, in how many hours will the tank be full?
Show answer & explanation
Correct answer: B
Explanation
Given:
Pipe P fills the tank = 12 hours
Pipe Q empties the tank = 18 hours
P's rate = 1/12
Q's rate = −1/18
Combined rate = 1/12 − 1/18
= 3/36 − 2/36
= 1/36
Time = 1 ÷ (1/36) = 36 hours