Pipes - Cistern

1 )

Two pipes B and F can fill the tank in 10 hours and 15 hours, respectively. If both the pipes are opened along with an outlet pipe M, then the tank is filled in 30 hours. Help me to find out how much times will the outlet pipe take to empty the full tank.

2 )

Three pipes A, B and C can fill a tank in 15 minutes, 20 minutes and 30 minutes respectively. The pipe C is closed 6 minutes before the tank is filled. In what time the tank will be full?

3 )

One filling pipe A is 5 times faster than second filling pipe B. If B can fill a cistern in 36 minutes, the find the time when the cistern will be full if both fill pipes are opened together.

4 )

Pipe A can fill an empty tank in 30 hours while B can fill it in 45 hours. Pipe A and B are opened and closed alternatively i.e., first pipe A is opened, then B, again A and then B and so on for 1 hour each time without any time lapse. In how many hours the tank will be filled if it was empty, initially?

5 )

A cistern can be filled by two taps A and B coming from the same main pipeline in 20 and 30 minutes respectively. Both the taps are opened at the same time but due to partial closing of a valve in the main pipeline, tap A was supplying only 4/5th of its capacity and tap B, 5/6th of its capacity. After some time, the valve in the main pipeline was opened fully thereby enabling the two taps to supply at full capacity. It took another 5 minutes to fill the cistern completely. How long (approx) was it before the valve on the main pipeline opened?