By mixing 70% and 60% acid solution and adding 2 kg of water, a 50% solution was obtained.

By mixing 70% and 60% acid solution and adding 2 kg of water, a 50% solution was obtained. If instead of 2kg of water we add 2kg of 90% acid solution, we get 70% solution How many kg of 70% acid solution were used for the mixture?

Let’s immediately introduce two variables to solve the problem:

Let the mass of the first solution be m, the mass of the second solution n.

Based on the conditions of the problem, we will compose and solve a system of two equations:

0.7 * m + 0.6 * n = 0.5 * (m + n + 2);

0.7 * m + 0.6 * n + 1.8 = 0.7 * (m + n + 2);

0.7 * m + 0.6 * n = 0.5 * m + 0.5 * n + 1;

0.7 * m + 0.6 * n + 1.8 = 0.7 * m + 0.7 * n + 1.4;

0.1 * n = 0.4;

n = 4 kg is the mass of the second solution.

0.7 * m + 2.4 = 0.5 * (m + 6);

0.7 * m + 2.4 = 0.5 * m + 3;

0.2 * m = 0.6;

m = 3 kg is the mass of the first solution.