Pipe A can fill a tank in 10 hours, pipe B in 15 hours and pipe C in 30 hours. If all the pipes are open, in how many hours will the tank be filled?  Choose the correct choice from the following:
A) 2
B) 2.5
C) 3
D) 5
E) None
Sol.   Part filled by (A + B + C) in 1 hour = (1/10 + 1/15 + 1/30) = 1/5.   âˆ´ All the three pipes together will fill the tank in 5 hours.   Answer 5
<result>D</result>
Pipe A can fill a tank in 10 hours, pipe B in 15 hours and pipe C in 30 hours. If all the pipes are open, in how many hours will the tank be filled?