To 200 g of a 10% solution add 300 g of a 15% salt solution. Calculate the percentage of the new solution.

Given:

m (1st salt) = 200 g

w% (1st salt) = 10%

m (2nd salt) = 300 g

w% (2nd salt) = 15%

To find:

w% (final solution) -?

Decision:

1) Find the mass of salt in the first solution:

m (salt) = 200 g * 0.1 = 20 g;

2) Find the mass of salt in the second solution:

m (salt) = 300 g * 0.15 = 45 g;

3) Find the mass of the solution after adding the second solution to the first:

m (solution) = 200 g + 300 g = 500 g;

4) Find the mass of salt after mixing the solutions:

m (salt) = 20 g + 45 g = 65 g;

5) Find the mass fraction of salt in the resulting solution:

w% (salt) = m (salt): m (solution) * 100% = 65 g: 500 g * 100% = 13%.

Answer: w% (salt) = 13%.