  # Two taps can separately fill a cistern in 10 min. and 15 min. respectively and when the waste pipe is open...

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Two taps can separately fill a cistern in 10 min. and 15 min. respectively and when the waste pipe is open, they can together fill it in 18 min. How much time full cisterm can be emptied by the waste pipe? posted Mar 8, 2016

The two taps can together fill the cistern in 6 mimutes.
(100/10 + 100/15) * N(minutes) = 100
Solving the equation, N= 6 minutes
In 18 minutes, the two taps can fill the cistern three times. In order to leave it full while the waste pipe is open, it means the full cistern is emptied twice. Therefore the answer is 18/ 2 = 9 minutes answer Mar 10, 2016 by anonymous

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