Two pipes P and Q can fill a tank in 10 hours and 15 hours respectively. If both pipes are opened simultaneously, how much time will be taken to fill the tank? Answers.
A) 4 hours 20 min  B) 5 hours 49 min  C) 3 hours 50 min  D) 6 hours  E) 3 hours 42 min
Explanation:   Part filled by P in 1 hour = 1/10   Part filled by Q in 1 hour = 1/15   Part filled by (P + Q) in 1 hour = ( 1/10 + 1/15) = (5/30) = 1/6   Time taken to fill the tank is  (6/1)= 
<gadget id="calculator"> (6/1)</gadget>
<output>6</output>
6 hrs   ANSWER 6 hours
<result>D</result>
Two pipes P and Q can fill a tank in 10 hours and 15 hours respectively. If both pipes are opened simultaneously, how much time will be taken to fill the tank?