Pipe P can fill a tank in 8 hours, pipe Q in 12 hours and pipe R in 20 hours. If all the pipes are open, in how many hours will the tank be filled? Pick: A) 2 hours B) 2.4 hours C) 3.8 hours D) 3.5 hours E) 4.5 hours
Explanation:   Part filled by (P + Q + R) in 1 hour = (1/8 + 1/12 + 1/20) = 31/120   All the three pipes together will fill the tank = 120/31 = 3.8 hours   ANSWER 3.8 hours
<result>C</result>
Pipe P can fill a tank in 8 hours, pipe Q in 12 hours and pipe R in 20 hours. If all the pipes are open, in how many hours will the tank be filled?