1)

A pipe can fill a tank in 12 minutes and another pipe in 15 minutes. But the third pipe can empty it in 6 minutes. The first two pipes are kept open for 5 minutes in the beginning and then the third pipe is also opened. In what time is the cistern emptied?

2)

Two taps can separately fill a cistern in 10 minutes and 15 minutes respectively. When the waste pipe is open, they can together fill it in 18 minutes. In how many minutes will the waste pipe can empty the full cistern?

3)

A tank is normally filled by one pipe A in 20 min and pipe B in 25 min. Both the pipes are kept open for 5 min and then pipe B is closed. In how many more minutes will the tank be fully filled?

4)

Pipe A usually fills a tank in 2 hours. On account of a leak at the bottom of the tank, it takes pipe A 30 more minutes to fill the tank. How long will the leak take to empty a full tank if pipe A is shut?

5)

A tank is fitted with 8 pipes, some of these fill the tank while some of these empty the tank. Each of the pipes that fills the tank fill it in 8 hours, while each of those that empty the tank empties it in 6 hours. If all the pipes are kept open when the tank is full, it will take 6 hours to drain the complete tank. How many of these are filling pipes?

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