13.310. There is scrap steel of two grades with nickel content of 5 and $40 \%$. How much of each of these grades of metal is needed to obtain 140 tons of steel with a $30 \%$ nickel content?
Solution.

Let $x, y$ be the mass of each type of metal taken. According to the condition

![](https://cdn.mathpix.com/cropped/2024_05_21_3edb7be591bff54ce350g-1200.jpg?height=167&width=1116&top_left_y=845&top_left_x=92)

Answer: 40 and 100 tons.