Pipes A and B can fill a tank in 3 and 5 hours. Pipe C can empty it in 12 hours. If all pipes are opened together, then the tank will be filled in?  Answers
A) 60/17 hr B) 12/19 hr C) 20/9 hr D) 9/20 hr E) 63/19 hr
Net part filled in 1 hour = 1/3 + 1/5 - 1/12 = 9/20   The tank will be full in 20/9 hr   Answer is 20/9 hr
<result>C</result>
Pipes A and B can fill a tank in 3 and 5 hours. Pipe C can empty it in 12 hours. If all pipes are opened together, then the tank will be filled in?