Question

There are two taps In a water tank. One can fill the tank completely in 4 minutes and the other can empty the full tank in 9 minutes. If both the taps are opened together, how much time will be required to fill the tank?

Answer 1

Work done by tap 1 in 1 min = 1/4
Work done by tap 2 in 1 min=1/9
Work done by tap 1 and tap 2 in 1 min = 1/4 + 1/9 =(9+4)/36=13/36
The tank will be filled in 36/13 min