One pipe can fill a tank in 60 minutes and another pipe can fill it in 50 minutes .If these two pipes are open and a third pipe is draining water from the tank ,it take 35 minutes to fill the tank .How long will it take the third pipe alone to empty the tank?

Answer 1

how much of the tank's volume is filled/drained each minute?

1/60 + 1/50 - 1/x = 1/35
1/x = 17/2100
So, it will take 2100/17 = 123.5 minutes