40 ml of acid was added to a 200 ml acid solution, after which the acid content

40 ml of acid was added to a 200 ml acid solution, after which the acid content in the solution increased by 5%. How much acid was in the solution initially?

Let’s denote by the unknown variable x ml – there was acid initially.

Then x + 40 ml – there was acid in the new solution.

240 ml – there is a new solution.

((x + 40) / 240) * 100% – the percentage of acid in the new solution.

(x / 200) * 100% – the percentage of acid in the initial solution.

((x + 40) / 240) * 100 – 5 = (x / 200) * 100;

(10x + 400 – 120) / 24 = x / 2;

10x + 280 = 12x;

2x = 280;

x = 140 ml – there was acid initially.