Pipe A can fill a tank in 9 hours, pipe B in 12 hours, and pipe C in 18 hours. If all the pipes are open, in how many hours will the tank be filled? Answers
A) 2
B) 3
C) 4
D) 5
E) 6
The part filled by A + B + C in 1 hour   = 1/9 + 1/12 + 1/18   = 9/36 = 1/4   All the three pipes together will fill the tank in 4 hours.   The answer is 4.
<result>C</result>
Pipe A can fill a tank in 9 hours, pipe B in 12 hours, and pipe C in 18 hours. If all the pipes are open, in how many hours will the tank be filled?