a tap can fill a tank in 15 minutes .another tap can empty it in 20 minutes.Initially the tank is empty,if both the taps start functioning the same time,when will the tank become fill?

Answer 1

each minute the tank

gains 1/15
loses 1/20

So, the net gain in volume is

1/15 - 1/20 = 1/60

So, it will take 60 minutes to fill up.

Answer 2

60 min