SOLUTION: How much gold valued at $12 per gram must be mixed with silver valued at $.80 per gram to obtain 20g of an alloy worth $5 per gram?
I set up the equations as s= silver g= gold
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Question 394370:  How much gold valued at $12 per gram must be mixed with silver valued at $.80 per gram to obtain 20g of an alloy worth $5 per gram?
I set up the equations as s= silver g= gold
s + g = 20
.8s + 12g = 5  I get s= 20.98 g = -.98
This doesn't seem right.  Can you please help? 
Answer by lwsshak3(11628)   (Show Source): You can put this solution on YOUR website!
 How much gold valued at $12 per gram must be mixed with silver valued at $.80 per gram to obtain 20g of an alloy worth $5 per gram?
let x = grams of gold used
then, 20-x = grams of silver used
note that the number of grams of the alloy must add up to the weight of the silver and gold used, ie, x+(20-x) = 20 
we then set up an equation, equating cost,($/gram * no. of grams)
12x+.8(20-x)=5*20
12x+16-.8x=100
11.2x=100-16=84
    x=84/11.2
    x=7.5 grams (gold used)
 20-x=12.5 grams (silver used)
ans:grams of gold that must be mixed with silver = 7.5 
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