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sterling silver is an alloy of 92.5% silver 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?

is the equation for copper 0.075(15 + s) = 3 + s?

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.

Step-by-step explanation: