Question

Because of a leak a tank which usually is filled in 3 hrs how takes 3.5 hrs to be filled The leak alone alone will empty the filled tank in

• A. 18 hrs
• B. 21 hrs
• C. 15 hrs
• D. Cannot be determined

Answer 1

The correct option is B 21 hrs

Work done for 1 hour without leak $=\frac{1}{3}$
Work done with leak in 1 hr$=\frac{2}{7}$
Work done by leak in 1 hr$=\frac{1}{3}-\frac{2}{7}=\frac{1}{21}$
So tank will be empty by the leak in 21 hours