How many ounces of pure gold are in an 18 karat gold chain that weighs 2.8 ounces?

Pure gold is 24 Karat's so the ratio of purity 18 karat gold is:
(Number of Karats of Gold chain)/(Number of Karats of pure Gold)
this will give us:
18/24
=3/4 
The weight of pure gold in 18 Karat Gold will be:
(ratio of purity)×(Total weight of chain)
=3/4×18
=13 1/2 ounces
=13.5 ounces.

18 karat gold contains 75% gold, and 25% other metals in the alloy. 75% of 2.8 ounces yields a gold content of 2.1 ounces. Multiplying .75 times 2.8 will yield the correct result.

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