Two pipes P and Q can fill a tank in 10 hours and 14 hours respectively. If both pipes are opened simultaneously, how much time will be taken to fill the tank?  Pick one.
A) 4 hours 20 min
B) 5 hours 49 min
C) 3 hours 50 min
D) 3 hours 22 min
E) 3 hours 42 min
Explanation:   Part filled by P in 1 hour = 1/10   Part filled by Q in 1 hour = 1/14   Part filled by (P + Q) in 1 hour = ( 1/10 + 1/14) = (6/35)   Time taken to fill the tank is (35/6) = 5 hours 49 min   ANSWER 5 hours 49 min
<result>B</result>
Two pipes P and Q can fill a tank in 10 hours and 14 hours respectively. If both pipes are opened simultaneously, how much time will be taken to fill the tank?