The pump used to fill the water tank on a fire truck takes 40 minutes to fill the tank. If the pump sending water to the hose is on, it takes 60 minutes to fill the tank. If the pump filling the water tank is off, how long does the pump sending water to the hose take to empty the tank?

Question

anonymous · Answer

120 , 60 , 30 , 24

mathstudent55 · Answer

In 1 minute, the filling pump fills 1/40 of the tank.
In 1 minute, the emptying pump does 1/x of the emptying. 
With both pumps on, in 1 minute, 1/60 of the tank is filled.

1/40 - 1/x = 1/60