13.231. Two grades of cast iron with different percentages of chromium were alloyed. If one grade is taken in 5 times the amount of the other, the percentage of chromium in the alloy will be twice the percentage of chromium in the smaller of the alloyed parts. If, however, equal amounts of both grades are taken, the alloy will contain $8 \%$ chromium. Determine the percentage of chromium in each grade of cast iron.
## Solution.

Let $x \%$ be the chromium content in one alloy, and $y \%$ in the second, i.e., $x$ kg of chromium in 1 kg of cast iron of one type, and $y$ kg in 1 kg of the other type.

According to the problem, we have $\left\{\begin{array}{l}5 x+y=6 \cdot 2 y, \\ x+y=2 \cdot 0.08,\end{array}\right.$

from which $x=0.11=11 \%, y=0.05=5 \%$.

Answer: 5 and $11 \%$.