SOLUTION: A goldsmith needs 120 grams of gold alloy, of 75% pure gold. Only two alloys of gold are available, the first being 80% pure gold and the other 60% pure gold. How many grams of 80%

Question 998304: A goldsmith needs 120 grams of gold alloy, of 75% pure gold. Only two alloys of gold are available, the first being 80% pure gold and the other 60% pure gold. How many grams of 80% pure gold must he use to suit his requirements?

Answer by addingup(3677) (Show Source): You can put this solution on YOUR website!
mix .80 and .60 to get 120 at .75
x+y= 120 Subtract y from both sides:
x= 120-y We'll use this value for x in the formula below:
-------------------
.80x+.60y= .75(120) Substitute for x:
.80(120-y)+.60y= .75(120) Let's multiply to get rid of parenthesis:
96-.80y+60y= 90 Subtract 96 on both sides:
-.80y+60y= -6 Add on left:
-.20y= -6 Divide both sides by -.20:
y= -6/-.20 When you divide, remember that - and - = +
y= 30 grams will be at 60% and
120-30= 90 grams will be at 80%

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