An alloy weighing 800g contains 15% copper. How much copper must be added to this alloy to make it 20% copper

| May 16, 2021 | education

1. Determine how many percent is the mass of impurities in the alloy. To do this, we take the mass of the entire alloy as 100% and subtract the percentage of copper from it:
100% – 15% = 85%.
2. Determine the weight of impurities in the alloy. To do this, the mass of the alloy must be multiplied by the percentage of impurities in the alloy and divided by 100%:
800 g * 85% / 100% = 680 g.
3. Determine the percentage of impurities in the new alloy. To do this, we take the mass of the whole new alloy as 100% and subtract the percentage of copper from it:
100% – 20% = 80%.
4. Determine the mass of the new alloy:
680 g * 100% / 80% = 850 g.
5. Determine how much you need to add a gram of copper to get a 20% alloy:
850 g – 800 g = 50 g.
Answer: 50 g.



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