Two pipes can fill a tank in 14 and 12 hours, while third pipe will make the tank empty in 20 hours. If all three pipes operate simultaneously. In how many hours the tank will be filled ? Choose the most appropriate option
A) 5.5 Hours  B) 7.5 Hours  C) 8.5 Hours  D) 9.5 Hours  E) 6.5 Hours
In 1 hour it fill 1/14 + 1/12 - 1/20 = 2/19   So fill tank fill up in 19/2= 
<gadget id="calculator">19/2</gadget>
<output>19/2 = around 9.5</output>
9.5 Hours   ANSWER:9.5 Hours
<result>D</result>
Two pipes can fill a tank in 14 and 12 hours, while third pipe will make the tank empty in 20 hours. If all three pipes operate simultaneously. In how many hours the tank will be filled ?