SOLUTION: How many g of gold should a coin of 56% gold be if when combined with a 7 g 100% gold necklace, it forms a metal that is 67% gold?

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Question 944486: How many g of gold should a coin of 56% gold be if when combined with a 7 g 100% gold necklace, it forms a metal that is 67% gold?

Answer by vleith(2983) About Me  (Show Source):
You can put this solution on YOUR website!
Let the gold coin's weight be represented by C.
You are told the coin is 56% gold. That gold is then melted with 7g of pure gold. So how much many grams does the coin weigh if the total at the end is 67% gold by weight?
%28C%2A0.56%29+%2B+%287%2A1%29+=+%287%2BC%29%2A+0.67
0.56C+%2B+7+=+%287%2A0.67%29+%2B+0.67C
7+-+%287%2A0.67%29+=+0.67C+-+0.56C
7+-+4.69+=+0.11C
2.31%2F0.11+=+C
21=C
So the original coin weighs 21 grams