Question 701319
 British sterling silver is a copper-silver alloy that is 7.5% copper by weight.
 How many grams of pure copper and how many grams of British sterling silver should be used to prepare 200 grams of a copper-silver alloy that is 10% copper by weight?
:
let c = amt of pure copper required
let s = amt of 7.5% copper which Br Sterling
:
c + s = 200
s = (200-c)

A mixture equation based on amt of copper
1c + .075s = .10(200)
Replace s with (200-c)
c + .075(200-c) = .10(200)
c + 15 - .075c = 20
c - .075c = 20 - 15
.925c = 5
c = 5/.925
c = 5.4 grams of pure copper
then find s
200-5.4 = 194.6 grams of Br Sterling
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I just noticed you only wanted the equations. Sorry!