A cistern is normally filled in 8 hrs,but takes 2 hrs longer to fill because of a leak on its bottom,if Cistern is full ,how much time citern would empty?  Pick:
A) 10 hours	B) 20 hours	C) 30 hours	D) 40 hours	E) 50 hours

Rationale: if leakage / hour = 1 / x , then 1 / 8 - 1 / x = 1 / 10 , solving 1 / x = 1 / 40 so in 40 hours full cistern will be empty . answer : d
Answer: D