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?

0 votes

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?

0 votes

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

...