Pipes A and B can fill a tank in 11 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  Choices.
A) 1 13/17 hours  B) 2 8/11 hours  C) 3 9/17 hours  D) 5 17/23 hours  E) None
Solution   Net part filled in 1 hour	= (1/11 + 1/6 -1/12)   = 23/132.   Therefore, the tank will be full in 132/23 hrs.	â€¹=â€º 5 17/23 hrs.   Answer 5 17/23 hours
<result>D</result>
Pipes A and B can fill a tank in 11 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