The mass of the copper-zinc alloy is 10 kg. How much zinc is contained in an alloy containing 20% copper.

In order to find how much zinc is contained in the alloy, we must make up and decide the proportion.

But first of all, let’s look at the condition of the problem. It says that the mass of a copper-zinc alloy is 10 kg. It is also known that the alloy contains 20% copper.

Let’s start by taking as 100% 10 kg of an alloy of copper and zinc, and for x kg we denote the weight of zinc in the alloy.

The percentage of zinc in the alloy: 100 – 20 = 80%.

We make up the proportion.

10 kg of alloy – 100%;

x kg of alloy – 80%;

10 / x = 100/80;

x = (10 * 80) / 100 = 800/100 = 8 kg of zinc in the alloy.