A 56-litre mixture contains milk and water in the ratio $5 : 2$. How much milk must be added to make the ratio $3 : 1$?

Explanation

1. 01

   Milk = $\frac{5}{7} \times 56 = 40$ litres; water = 16 litres.

2. 02

   Water stays 16, so milk must become $3 \times 16 = 48$ litres.

3. 03

   Milk to add = $48 - 40 = 8$ litres.