The mass of copper and zinc alloy is 2kg. and they are 75% copper. How much zinc do you need

The mass of copper and zinc alloy is 2kg. and they are 75% copper. How much zinc do you need to add to make 60% copper?

From the very beginning, we will determine how much copper is in the alloy. T. to. according to the condition of the problem, the mass of the alloy is 2 kg, a% of the copper content is 75%, then the mass of copper in the alloy is:

2 * 75% = 2 * 0.75 = 1.5 (kg).

In the new alloy, the same 1.5 kg of copper should already be 60%. Let’s denote the mass of zinc to be added to the alloy as x. Then you can make up the proportion:

1.5 kg of copper is 60%;

(2 + x) is 100%.

We get:

1.5 * 100 = (2 + x) * 60;

150 = 120 + 60 * x;

60 * x = 30 | : 60;

x = 0.5 (kg).

Answer: 0.5 kg of zinc.