Pipes A and B can fill a tank in 9 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in  Choose the correct choice from the following options: A) 1 13/17 hours B) 2 8/11 hours C) 3 9/17 hours D) 5 1/7 hours E) None
Solution   Net part filled in 1 hour	= (1/9 + 1/6 -1/12)   = 7/36.   Therefore, the tank will be full in 36/7 hrs.	â€¹=â€º 5 1/7 hrs.   Answer 5 1/7 hours
<result>D</result>
Pipes A and B can fill a tank in 9 and 6 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in