A leak empties a full tank in 8 hours. When a tap letting in 6 litres a minute is also opened, the full tank empties in 12 hours. How many litres does the tank hold?

Explanation

1. 01

   The tap adds $6 \times 60 = 360$ litres an hour. For a capacity $C$: $\frac{C}{8} - 360 = \frac{C}{12}$.

2. 02

   $C\left(\frac{1}{8} - \frac{1}{12}\right) = 360$, so $\frac{C}{24} = 360$ and $C = 8{,}640$ litres.