Pipes and Cistern - General Questions

Pipes A and B can fill a tank in 15 and 16 minutes, and pipe C can empty it in 37 minutes. If all three are opened together, how long will it take to fill the tank?

Two pipes A and B can fill a tank in 7 hours and 27 hours respectively. If both are opened together, how long will they take to fill the tank?

A pipe can fill a tank in 13 hours and another pipe can empty it in 34 hours. If both are opened together, in how much time will the tank be filled?

A pipe fills a tank in 12 hours. Because of a leak at the bottom it takes 14 hours. If the tank is full, in how much time will the leak empty it?

Two pipes A and B can fill a tank in 26 hours and 15 hours respectively. If both are opened together, how long will they take to fill the tank?