1) An electric pump can fill a tank in $3$ hours. Because of a leak in the tank, it took $3\frac{1}{2}$ hours to fill the tank. If the tank is full, how much time will the leak take to empty it ? A) 21 hours B) 20 hours C) 30 hours D) 40 hours E) 50 hours Answer: Option AExplanation:Work done by the leak in 1 hour $=\left[\frac{1}{3}-\frac{1}{\left(\frac{7}{2}\right)}\right]$ $=\frac{1}{3}-\frac{2}{7}$ $=\frac{1}{21}$ The leak will empty the tank in 21 hours.
