List of top General Management Questions on Pipe and Cistern

Two pipes A and B can fill a tank in 10 hours and 12 hours respectively. A third pipe C can empty the tank in 20 hours. If all three pipes are opened and function simultaneously, how much time (in hours) will the tank take to be full?
Two pipes X and Y together can fill a cistern in 4 hours. Had they been opened separately, then Y would have taken 6 hours more than X to fill the cistern. How much time (in hours) will be taken by X alone to fill the cistern?
Three pipes A, B and C can fill a tank in 10, 15 and 20 hours respectively. Pipe A was opened at 6 AM, pipe B at 7 AM and pipe C at 8 AM. At what time was the tank completely filled?
A tank has four pipes P1, P2, P3, P4. The tank can be filled in 15 minutes by pipes P1, P2, P3 together. It can be filled in 20 minutes by pipes P1, P2, P4 together and it can be filled by pipes P1 and P3 together in 30 minutes. If all the pipes are opened together, then in how much time will the tank be filled?