A cistern is normally filled in 4 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?
Choose the correct choice from the following answers.
A) 10 hours
B) 20 hours
C) 30 hours
D) 40 hours
E) 12 hours

Rationale: "if leakage / hour = 1 / x , then 1 / 4 - 1 / x = 1 / 6 , solving 1 / x = 1 / 12 so in 12 hours full cistern will be empty . answer : e"
Answer: E