Question:
Tick (✓) the correct answer:
A pump can fill a tank in 2 hours. Due to a leak in the tank it takes $2 \frac{1}{3}$ hours to fill the tank. The leak can empty the full tank in
(a) $2 \frac{1}{3}$ hours
(b) 7 hours
(c) 8 hours
(d) 14 hours
Solution:
(d) 14 hours
A pump can fill a tank in 2 hours.
Part of the tank filled by the pump in one hour $=\frac{1}{2}$
Suppose the leak empties a full tank in x hours.
Part of the tank emptied by the leak in one hour $=-\frac{1}{x}$
Part of tank filled in one hour $=\frac{1}{2}-\frac{1}{x}=\frac{3}{7}$ (given)
$\frac{1}{\mathrm{x}}=\frac{1}{2}-\frac{3}{7}=\frac{7-6}{14}=\frac{1}{14}$
$\mathrm{x}=14$ hours