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?
8 hours
12 hours
24 hours

Question

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?
8 hours
12 hours
24 hours

anonymous · Answer

ok if the tank can be filled by one pipe (lets call it A) in 4 hours,
how much tank can it fill in 1 hour?any idea?

anonymous · Answer

ok a Hint:  if the tank can be filled by one pipe (lets call it A) in X hours, it'll fill 1/X part of the tank in 1 hour...do you follow?

hero · Answer

Pipe A = 4 hr
Pipe B = 6 hr
Pipe C = 3 hr

$$\frac{abc}{ac + bc  - ab}$$
$$\frac{(4)(6)(3)}{(4)(3) + (6)(3) - (4)(6)} = \frac{72}{6} = 12$$