Solute in 200 g of 30% solution $=60$ g
Solute in 300 g of 20% solution $=60$ g
total grams of solute $=120$ g
total grams of solution $=200+300=500$ g
% of solute in the final solution $=\frac{\text{Wt. of solute}}{\text{Wt. of solution}}\times 100$
% of solute in the final solution $=\frac{120}{500}\times 100=24\mathrm{\%}$