A pump can fill a tank with water in 1 hour. Because of a leak, it took $1\frac{1}{3}$hours to fill the tank. In how many hours can the leak alone drain all the water of the tank when it is full?

5 1 2 4

4

A = 1 hour, A + B = \( {1 }_{3 }^{ 1} \) hrs, ⇒ A + B = 3,  (Efficiency) ⇒ 4 + B = 3, ⇒ B = -1, Time taken by B to completely empty the cistern alone = \(\frac{4}{1}\) = 4 hrs.