A tray holds 40 kg of brine that is 5% salt. How many kg of water must evaporate for the brine to become 8% salt?

Explanation

1. 01

   Salt = $0.05 \times 40 = 2$ kg, which stays the same.

2. 02

   For 2 kg to be 8%, the total must be $\frac{2}{0.08} = 25$ kg.

3. 03

   Water evaporated = $40 - 25 = 15$ kg.