Question

there is a tank and two pipes a and b.a can fill the tank in 25 minutes and b can empty the tank in 20 minutes.if both pipes are opened at same time.how much time required the tank can fill?

Answer 1

In one minute :

a fills 1/25 of the tank.

b empties 1/20 of the tank.

In one minute the amount of water in the tank is :

1/25 - 1/20 = - 1/100 of the tank

This gives - 100 minutes

This means that every minute we will have a negative amount meaning no water in the tank.

Therefore the tank can never get full when the two taps are opened.

In essence tap B is emptying the tank faster than tap A is filling the tank.