Use ratios:
Grams:Total SF: 100 divided by 25 = 4
NICKEL=
9 grams: 25grams = 36% : 100%
Multiply 9grams of nickel by 4 (the scale facotr) to get the percentage of nickel in the coin
COPPER=
16 grams: 25grams = 64% :100%
Multiply 16 grams of copper by 4 (the scale factor) to get the percentage of copper in the coin
ANSWER: 26% of nickel and 64% of copper is in a coin
