Question

The percentage (by mass) concentration of a solution obtained by mixing $300$ g of a $25$% (solution $I$) and $400$ g of a $40$% (solution $II$) by mass is (as the nearest integer):

Answer 1

Mass of solution $I$ $=$ $300$ g

$\therefore$ Mass of solute in solution $I$ $=\frac{25\times 300}{100}=75$ g

Mass of solution $II$ $=$ $400$ g

Mass of solute in solution $II$ $=\frac{40\times 400}{100}=160$ g

Now, total mass of solute in solutions after mixing $=75+160=235$ g

Total mass of solution after mixing $=300+400=700$ g

% by mass $=\frac{235}{700}\times 100=33.57$%

So, the answer is $34\%$.