From the 20% brine solution, 25% of the water contained in it was evaporated. Find the percentage

From the 20% brine solution, 25% of the water contained in it was evaporated. Find the percentage of the resulting solution.

Let us denote by p the mass of the initial solution, expressed in kilograms.

According to the condition of the problem, the concentration of the initial solution was 20 percent, therefore, the initial solution contained 100 – 20 = 80% water, which was (80/100) * p = 0.8 * p kg.

After 25% of water was evaporated, which was (25/100) * 0.8 * p = 0.25 * 0.8 * p = 0.2 * p kg, the mass of the resulting solution turned out to be p – 0.2 * p = 0.8 * p, and its concentration :

100 * (p – 0.8 * p) / (0.8 * p) = 100 * 0.2 * p / (0.8 * p) = 100 * 0.2 / 0.8 = 100 * 0.2 / 0.8 = 100 * 2/8 = 100 / 4 = 25%.

Answer: 25%.