The first alloy contains 60% copper (its mass is 300 kg), the second 45%.

The first alloy contains 60% copper (its mass is 300 kg), the second 45%. How much kg do you need to take from the second piece of alloy to get an alloy containing 56% copper?

Let’s find the amount of pure copper in the first alloy:

300 * 60/100 = 180 kg.

Let us take the mass of the second piece as x, then:

x * 45/100 – the amount of copper in the second alloy;

180 + x * 45/100 – the amount of copper in the resulting alloy;

300 + x is the mass of the resulting alloy.

Since the concentration of copper in the resulting alloy is 10 kg, we get the equation:

(180 + 0.45x): (300 + x) = 0.56;

180 + 0.45x = 0.56 * (300 + x);

180 + 0.45x = 168 + 0.56x;

0.11x = 22;

x = 10.

Answer: You need to add 10 kg of the second alloy.