A cistern is fille in 8 hours and it takes 12 hours when there is a leak in its bottom. If the cistern is full, in what time shall the leak empty it?	Choose the correct choice.
A) 22 hours	B) 21 hours	C) 24 hours	D) 23 hours	E) 25 days

Rationale: explanation : work done by 1 hour by filling pipe = 1 / 8 work done by 1 hour by the leak and the filling pipe = 1 / 12 work done by 1 hour by the leak = 1 / 8 – 1 / 12 = 1 / 24 hence the leak can empty it in 24 hours . answer : option c
Answer: C