Arrange the formulas of the substances CuFeS2, Cu2S, Cu2O in the order of decreasing mass fraction of copper in them

The mass fraction of an element (w) in a substance is expressed by the formula:
W = (n * Ar / Mr) * 100%, where n is the number of atoms of the element, Ar is the relative atomic mass of the element, Mr is the relative molecular weight of the substance;
1) Mr (CuFeS2) = 64 + 56 +32 * 2 = 184
W (Cu) = (1 * 64/184) * 100%
W (Cu) = 34, 78%
2) Mr (Cu2S) = 64 * 2 + 1 * 32 = 160
w (Cu) = (2 * 64/160) * 100%
w (Cu) = 80%
3) Mr (CU2O) = 2 * 64 + 1 * 16 = 144
w (Cu) = (2 * 64/144) * 100%
w (Cu) = 88.89%
Answer: Let us arrange the substances in the order of decreasing mass fractions of copper in them: Cu2O – Cu2S – CuFeS2