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?
A. 8 hours
B. 12 hours
C. 24 hours

Answer 1

I think its B.  In 12 hrs, the tank will be filled with
all 3 pipes open

Answer 2

The correct answer would be 
B) 12 hours.