[Problems on Mixtures and Concentrations]

From two pieces of alloys (with different lead content) weighing 6 and 12 kg, pieces of equal mass were cut. Each of the cut pieces was melted with the remainder of the other piece, after which the percentage of lead in both alloys became the same. What are the masses of each of the cut pieces?
In each of the received pieces, the ratio of the first alloy to the second should be the same (namely $1: 2$, since the second alloy is twice as much). This means the cut piece constitutes $1 / 3$ of 12 kg (and $2 / 3$ of 6 kg).

## Answer

4 kg.