Pipe A can fill a tank in 5 hours, pipe B in 10 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) 3.5	E) None
Sol.   Part filled by (A + B + C) in 1 hour = (1/5 + 1/10 + 1/30) = 1/3.   ∴ All the three pipes together will fill the tank in 3 hours.   Answer 3
<result>C</result>
Pipe A can fill a tank in 5 hours, pipe B in 10 hours and pipe C in 30 hours. If all the pipes are open, in how many hours will the tank be filled?