A coin contains 1.25grams of nickel and 3.75 grams of copper, for a total weight of 555 grams.

What percentage of the metal in the coin is copper?

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If there is 3.75 grams copper for every 1.25 grams nickel, then we have 3.75 grams copper for every 3.75+1.25=5 grams of metal. As a result, 3.75/5=3/4 of the coin is copper. This is equal to 75 percent.