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[I absolutely don't get this, please help] Sterling silver is an alloy of 92.5% sliver and 7.5% copper by weight. You have 15 ounces of 800 grade silver which is 80% silver and 20% copper. How much pure silver should you add to the 800 grade to make sterling silver?​

1 Answer

3 votes

If
s is the amount of pure silver you add to the alloy, then the new alloy will have a total weight of
15+s oz. You want 92.5% of this alloy to be silver, so that the amount of silver in the new alloy is
0.925(15+s).

80% of the starting 15 oz alloy was silver; this comes out to 12 oz. To this amount we are adding
s. So


0.925(15+s)=12+s

and solving this tells you that you need to add
s=25 oz of silver to get the sterling silver alloy.

User Wogan
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