Two pipes can fill a tank in 10 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 correct choice from the following answers
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 1/10 + 1/12 - 1/20 = 8/60   So fill tank fillup in   60/8= 
<gadget id="calculator">  60/8</gadget>
<output>15/2 = around 7.5</output>
7.5 Hours   ANSWER:7.5 Hours
<result>B</result>
Two pipes can fill a tank in 10 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 ?