"Two pipes A and B can fill a tank in 15 hours and  20 hours respectively while a third
Channel: Doubtnut
Date: 2020-07-05

"Two pipes A and B can fill a tank in 15 hours and
  20 hours respectively while a third pipe C can empty the full tank in 25 hours.
  All the three pipes are opened in the beginning. After 10 hours C is closed.
  In how much time will the tank be full?
 `12\ h r s`
 b. `13\ h r s`
 c. `16\ h r s`
 d. `18\ h r s`"