A 300 g sample of refined copper has 3 % impurities by weight. After a refining process that removes 70 % of the impurities, what is the new purity percentage of the copper?

Step-by-step solution

1. Calculate initial impurity mass: $0.03\times 300=9$ g.
2. Determine impurities removed: $0.70\times 9=6.3$ g.
3. Compute remaining impurities: $9-6.3=2.7$ g.
4. Find new purity: $\frac{300-2.7}{300}\times 100=99.1\%$

Concept tested: Purity after purification

Published 16 October 2026 · How this solution was prepared and checked