11.

Pipe A can fill an empty tank in 6 hours and pipe B in 8 hours. If both the pipes are opened and after 2 hours pipe. A is closed, how much time B will take to fill the remaining tank?

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A water tap fills a tub in 'p' hours and a sink at the bottom empties it in 'q' hours. If p < q and both tap and sink are open, the tank is filled in 'r' hours; then

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• r = p  +q

• r = p  +q

Two pipes P and Q can fill a cistern in 12 and 15 min, respectively. If both are opened together and at the end of 3 min, the first is closed. How much longer will the cistern take to fill?

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• 5 min

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A tap can empty a tank in 30 min. A second tap can empty it in 45 min. If both the taps operate simultaneously, how much time is needed to empty the tank?

• 30 min

• 14 min

• 15 min

• 18 min

A pipe can fill a tank in x h and another can empty it in y h. They can together fill it in (y > x)

• x - y

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• y - x

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