13.289. There are two alloys consisting of zinc, copper, and tin. It is known that the first alloy contains $40 \%$ tin, and the second - $26 \%$ copper. The percentage of zinc in the first and second alloys is the same. By melting 150 kg of the first alloy and 250 kg of the second, a new alloy was obtained, in which there turned out to be $30 \%$ zinc. How much tin is contained in the newly obtained alloy?
## Solution.

Let $x$ be the percentage of zinc in the first alloy. According to the condition, $\frac{x}{100} \cdot 150+\frac{x}{100} \cdot 250=\frac{30}{100}(150+250)$, from which $x=30 \%$. Then in the second alloy, there is $100 \%-(26 \%+30 \%)=44 \%$ of tin, and the new

$$
\text { alloy contains } \frac{40}{100} \cdot 150+\frac{44}{100} \cdot 250=170 \text { (kg) of tin. }
$$

Answer: 170 kg.