Two pipes can fill a tank in 12 hours and 18 hours, respectively. A third pipe can empty the tank in 9 hours. If all three pipes are opened together, in how much time will the tank be filled?
Show answer & explanation
Correct answer: B
Explanation
Capacity of the first tap in 1 hour = 1/12 of the tank
Capacity of the second tap in 1 hour = 1/18 of the tank
Efficiency of the emptying tap in 1 hour = −1/9 of the tank
Total work =
= 1/36
That is, 1/36 of the tank will be filled in one hour.
Time to fill the entire tank = 36 hours