A 10% salt solution was mixed with a 30% salt solution and received 300 g of a 15% solution.

A 10% salt solution was mixed with a 30% salt solution and received 300 g of a 15% solution. How many grams of a 30% solution did you take for this?

Let us denote the mass of a 10% salt solution through x10, and the mass of a 30% salt solution through x30.

Then we can compose the following equations:

x10 + x30 = 300;

(10/100) * x10 + (30/100) * x30 = (15/100) * 300.

We solve the resulting system of equations.

Simplifying the second equation, we get:

10 * x10 + 30 * x30 = 15 * 300;

10 * x10 + 30 * x30 = 4500.

Substituting into the resulting equation the value x10 = 300 – x30 from the first equation, we get:

10 * (300 – x30) + 30 * x30 = 4500;

3000 – 10 * x30 + 30 * x30 = 4500;

20 * x30 = 4500 – 3000;

20 * x30 = 1500;

x30 = 1500/20 = 150/2 = 75.

Answer: 75 grams.