A 40-litre can holds milk and water in the ratio $3 : 1$. Anil draws out 8 litres and replaces them with water, then does the same once more. What percentage of the can is now water?

Explanation

1. 01

   Milk at first = $\frac{3}{4} \times 40 = 30$ litres.

2. 02

   Each operation keeps $\frac{40 - 8}{40} = \frac{4}{5}$ of the milk.

3. 03

   Milk left = $30 \times \left(\frac{4}{5}\right)^2 = 19.2$ litres, so water = $40 - 19.2 = 20.8$ litres.

4. 04

   Water % = $\frac{20.8}{40} \times 100 = 52\%$.