Pipe A can fill a tank in 8 hours, pipe B in 10 hours and pipe C in 40 hours. If all the pipes are open, in how many hours will the tank be filled?
Pick:  A) 2  B) 2.5  C) 3  D) 4  E) None
Sol.   Part filled by (A + B + C) in 1 hour = (1/8 + 1/10 + 1/40) = 1/4.   âˆ´ All the three pipes together will fill the tank in 4 hours.   Answer 4
<result>D</result>
Pipe A can fill a tank in 8 hours, pipe B in 10 hours and pipe C in 40 hours. If all the pipes are open, in how many hours will the tank be filled?