Question

How much salt should Ilya add to 810g of water to make 10% solution? How much solution will he make?
(grams)

Answer 1

Let the $x$ represent amount of salt in grams that Illya should add. Then, the following equation should be solved:
$\frac{810}{90}=\frac{x}{10}$
$\frac{x}{10}=9$
$x=9*10=90$

So, Illya should add 90g of salt to make 10% solution. The total solution that he make is 810g + 90g = 900g.