Two salt solutions were drained: 160 g of a 5% solution and 140 g of a 20% solution.

Two salt solutions were drained: 160 g of a 5% solution and 140 g of a 20% solution. Determine the mass fraction of a substance in a solution?

Given:
m1 solution (salt) = 160 g
ω1 (salt) = 5%
m2 solution (salt) = 140 g
ω2 (salt) = 20%

To find:
ω3 (salt) -?

Solution:
1) m1 (salts) = ω1 (salts) * m1 solution (salts) / 100% = 5% * 160/100% = 8 g;
2) m2 (salt) = ω2 (salt) * m2 solution (salt) / 100% = 20% * 140/100% = 28 g;
3) m3 (salt) = m1 (salt) + m2 (salt) = 8 + 28 = 36 g;
4) m3 solution (salt) = m1 solution (salt) + m2 solution (salt) = 160 + 140 = 300 g;
5) ω3 (salt) = m3 (salt) * 100% / m3 solution (salt) = 36 * 100% / 300 = 12%.

Answer: The mass fraction of salt is 12%.