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.

A. 16 hrs
B. 20 hrs
C. 25 hrs
D. 40 hrs

Work done by leak in 1 hour = (1/8 – 1/10) = 1/40

The leak will empty the cistern in 40 hours.