Merged two solutions of sulfuric acid: 240 g 30% and 180 g 5%. What is the mass fraction of acid in the resulting solution?

Given:
m1 solution (H2SO4) = 240 g
ω1 (H2SO4) = 30%
m2 solution (H2SO4) = 180 g
ω2 (H2SO4) = 5%
Find: ω3 (H2SO4) -?
Decision:
1) m1 (H2SO4) = ω1 (H2SO4) * m1 solution (H2SO4) / 100% = 30% * 240/100% = 72 g;
2) m2 (H2SO4) = ω2 (H2SO4) * m2 solution (H2SO4) / 100% = 5% * 180/100% = 9 g;
3) m3 (H2SO4) = m1 (H2SO4) + m2 (H2SO4) = 72 + 9 = 81 g;
4) m3 solution (H2SO4) = m1 solution (H2SO4) + m2 solution (H2SO4) = 240 + 180 = 420 g;
5) ω3 (H2SO4) = m3 (H2SO4) * 100% / m3 solution (H2SO4) = 81 * 100% / 420 = 19.3%.
Answer: Mass fraction of H2SO4 is 19.3%.