Pipes A and B can fill a tank in 20 minutes and 30 minutes, respectively. Meanwhile, a drainpipe C can empty the tank in 60 minutes. If all three pipes are opened simultaneously, how long will it take to fill the tank?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. 15 min.
Pipe A's rate = 1/20
Pipe B's rate = 1/30
Pipe C's rate = 1/60
Combined rate = 1/20 + 1/30 – 1/60 = 1/15
Time to fill tank = 1 ÷ (1/15) = 15 minutes