A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in?

Question: A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in?

Solution:
If a tap can fill a cistern in x hours, then the tank filled by the tap in 1 hour = 1/x of the total tank.
Part emptied by the leakage in 1 hour
= 1/8 - 1/10
= (5 - 4)/40
= 1/40

∴ The leakage will empty the cistern in 40 hours.