Pipe A fills a tank in 30 minutes. Pipe B lets in 5 litres a minute more than A and fills the tank in 20 minutes. What is the capacity of the tank?

Explanation

1. 01

   With capacity $C$, A gives $\frac{C}{30}$ and B gives $\frac{C}{20}$ litres a minute: $\frac{C}{20} - \frac{C}{30} = 5$.

2. 02

   $\frac{C}{60} = 5$, so $C = 300$ litres.