A container has 40 litres of a mixture of milk and water in the ratio $3 : 1$. How many litres of water must be added to make the ratio of milk to water $5 : 3$?

Explanation

1. 01

   Milk = 30 litres and water = 10 litres. The milk stays the same.

2. 02

   For milk : water = $5 : 3$, water must be $30 \times 3 \div 5 = 18$ litres.

3. 03

   Water to add = $18 - 10 = 8$ litres.