We mixed two solutions of 200 g of a 10% solution and 250 g of a 25% solution, then added 30 g.

We mixed two solutions of 200 g of a 10% solution and 250 g of a 25% solution, then added 30 g. How much water should be added to make the moss fraction of the solution 15%?

Given:
m1 solution (in-va) = 200 g
ω1 (in-islands) = 10%
m2 solution (in-va) = 250 g
ω2 (in-va) = 25%
m3 (in-va) = 30 g
ω4 (in-va) = 15%

To find:
m (H2O) -?

Decision:
1) m1 (in-va) = ω1 (in-va) * m1 solution (in-va) / 100% = 10% * 200/100% = 20 g;
2) m2 (in-va) = ω2 (in-va) * m2 solution (in-va) / 100% = 25% * 250/100% = 62.5 g;
3) m4 (in-va) = m1 (in-va) + m2 (in-va) + m3 (in-va) = 20 + 62.5 + 30 = 112.5 g;
4) m4 solution (in-va) = m4 (in-va) * 100% / ω4 (in-va) = 112.5 * 100% / 15% = 750 g;
5) m (H2O) = m4 solution (in-va) – m1 solution (in-va) – m2 solution (in-va) – m3 (in-va) = 750 – 200 – 250 – 30 = 270 g.

Answer: The mass of H2O is 270 g.