Pipe P can fill a tank in 3 hours, pipe Q in 9 hours and pipe R in 18 hours. If all the pipes are open, in how many hours will the tank be filled? Choose the correct choice from the following options: A) 2 hours B) 2.4 hours C) 3 hours D) 3.5 hours E) 4.5 hours
Explanation:   Part filled by (P + Q + R) in 1 hour = (1/3 + 1/9 + 1/18) = 1/2   2 hoursll the three pipes together will fill the tank = 2/1= 
<gadget id="calculator">2/1</gadget>
<output>2</output>
2 hours   2 hoursNSWER 2 hours
<result>A</result>
Pipe P can fill a tank in 3 hours, pipe Q in 9 hours and pipe R in 18 hours. If all the pipes are open, in how many hours will the tank be filled?