13.247. From milk with a fat content of $5 \%$, cottage cheese with a fat content of $15.5 \%$ is produced, leaving whey with a fat content of $0.5 \%$. How much cottage cheese can be obtained from 1 ton of milk?
Solution.

Let $x$ tons of cottage cheese with a fat content of $15.5\%$ be obtained, then $(1-x)$ tons of whey with a fat content of $0.5\%$ will remain. Therefore, in 1 ton of milk, there is

$$
\frac{15.5 x}{100}+\frac{0.5(1-x)}{100}=\frac{15 x+0.5}{100} \text { tons of fat. }
$$

According to the condition $\frac{15 x+0.5}{100}=\frac{5}{100}$, from which $x=0.3=300$ kg.

Answer: 300 kg.