A tap fills a cistern in 9 hours, but a crack at the bottom drains the full cistern in 15 hours. If the tap is opened with the crack unrepaired, how long will the empty cistern take to fill (in hours)?

Question

Accepted Answer

22.5. Net rate = 1/9 − 1/15 = 5/45 − 3/45 = 2/45 of the cistern per hour, so time = 45/2 = 22.5 hours.

A tap fills a cistern in 9 hours, but a crack at the bottom drains the full cistern in 15 hours. If the tap is opened with the crack unrepaired, how long will the empty cistern take to fill (in hours)?

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