Pipes A and B can fill a tank in 4 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 one:  A) 3 hrs  B) 3 9/77 hrs  C) 3 9/17 hrs  D) 3 9/27 hrs  E) 3 9/19 hrs
Net part filled in 1 hour = 1/4 + 1/6 - 1/12   = 4/12 = 1/3   The tank will be full in 3 hrs   3 hrsnswer:3 hrs
<result>A</result>
Pipes A and B can fill a tank in 4 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?