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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:

area of part 1:

a1=base*height/2=(8+2)*(8-2-2-1)/2=10*3/2=15 ft^2

area of part 2:

a2=length*width=(8+2)*1=10 ft2

area of part 3:

a3=length*width=8*2=16 ft2

total shaded area : a1+a2+a3=41 ft2

total area of the reactangle : a=16*8=128 ft2

total area of the nonshaded region : 128-41=87 ft2