The composition of copper and zinc with a total weight of 2 kg contains 72% copper.

The composition of copper and zinc with a total weight of 2 kg contains 72% copper. How much zinc must be added to this alloy to get a new alloy that contains 60% copper?

According to the condition of the problem, an alloy weighing 2 kg contains 72% copper, which means that the mass of copper in the alloy is:

2: 100 * 72 = 1.44 kg.

Suppose that the copper content in the alloy becomes 60%, x kg of zinc must be added to it.

Since the mass of copper does not change, we obtain the following equation:

1.44: (2 + x) = 60: 100,

1.44 = 2 * 0.6 + 0.6 * x,

0.6 * x = 1.44 – 1.2,

x = 0.24: 0.6,

x = 0.4 kg.

Answer: 0.4 kg.