A piece of brass weighing 5 kg contains 3 kg of copper. How much of this piece is copper?

The mass fraction of a substance is found by the formula: dry matter mass / mixture mass * 100. To find how much of this piece is copper, you need to divide the mass of copper by the mass of brass. 3/5 of the piece is copper. To find this as a percentage, you need to convert the fractional part to a decimal fraction by dividing in a column or simply multiplying the numerator and denominator by 10 or 100. We get 3/5 = 0.6. To find the percentage, it is enough to multiply this part by 100. We get 0.6 * 100 = 60%.
Answer: 60% of brass is copper.