A tank can be filled by one pipe in four hours and by a second pipe in six hours; and when it is full, the tank can be drained by a third pipe in three hours. If the tank is empty and all three pipes are open, in how many hours will the tank be filled?

Question

anonymous · Answer

let the tank be filled in x hours ,then
$$\frac{ x }{ 4 }+\frac{ x }{ 6 }-\frac{ x }{ 3 }=1$$
L.C.M. of 4,6,3=12
multiply by 12
3x+2x-4x=12
x=?