Nine red pipes and twelve blue pipes provide water to a swimming pool. A red pipe can fill the pool in $36$ hours whereas a blue pipe can fill it in $48$ hours. There was some problem with the water supply and some of the pipes did not supply water at all. As a result it took $50\%$ more time to fill the swimming pool. What could be the number of pipes that stopped working?

Two inlet pipes A and B can fill an empty tank in 22 and 33 hours respectively. They are opened together but pipe A is turned off 3 hours before the tank is filled. How many hours are required to fill the tank completely by both pipes?

Pipe A in comparison to pipe B fills a tank in one fourth time. Pipe C in comparison to pipe A takes 3 times more time to fill the tank. If the three pipes are opened together, the tank is filled in 24 hours. If Pipe C is not opened, how much time will it take to fill the tank?

Of the three pipes, the first two can fill an empty tank in 10.8 and 21.6 hours respectively, while the third pipe can empty the tank in 18 hours. If the tank is empty and all the three pipes are opened together then in how many hours will tank fill?

Two pipes separately take $5$ hours and $8$ hours respectively to fill a tank. The third pipe takes $3.2$ hours to drain out the water from the tank. How much time will all the three pipes take to fill the completely empty tank?