Question

The fill pipe for a tank can fill the tank in 15 min and the drain pipe can empty the tank in 10 min. If both pipes are accidentally opened, how long will it take to empty the full tank?

Answer 1

30 min

Explanation:

The tank can be filled in 15 min, this means that in one min, 1/15 of the tank can be filled.

The tank can be emptied in 10 min, this means that in one min, 1/10 of the tank can be emptied.

the outflow rate - the inflow rate = rate of emptying the tank

1/10 - 1/15 = 1/x

where x is the time it will take to empty the tank

solving, we'll have

1/30 = 1/x

the reciprocal of the equation gives

x = 30 min