An ingot of an alloy of copper and zinc weighing 36 kg contains 45% copper.

An ingot of an alloy of copper and zinc weighing 36 kg contains 45% copper. How much copper must be added to this piece so that the plucked alloy contains 60% copper?

First, find the weight of the copper in the starting alloy.

Multiply 36 kg by the percentage of copper.

36 * 45% / 100% = 36 * 0.45 = 16.2 kg.

We make a proportion in which we write down the required amount of copper as x kg.

Let 16.2 kg of copper refer to 45%, just as (16.2 + x) refers to 60%.

16.2 / 45% = (16.2 + x) / 60%.

45 * (16.2 + x) = 16.2 * 60.

729 + 45 * x = 972.

45 * x = 972 – 729.

45 * x = 243.

x = 243/45 = 5.4 kg.

100% – 60% = 40%.

5.4 / 0.4 = 13.5 kg.

Answer: For the alloy to have 60% copper, you need to add 13.5 kg.