Iron with carbon forms a carbide, in which the mass fraction of iron is 93.3%. Determine the simplest formula of this carbide.

Let us denote: x is the number of iron atoms in the carbide, y is the number of carbon atoms in the carbide. The molecular weight of the carbide is denoted by M.
The relative atomic mass of iron is 56, carbon is 12.
Let’s compose the following expressions:
0.933 = 56 * x / M;

0.067 = 12 * y / M;

Let us express the molecular weight from each expression:
M = 56x / 0.933 = 60x;

M = 12y / 0.067 = 179.1y;

When equating the obtained expressions, approximate values were obtained: x = 3, y = 1. The carbide formula is Fe3C.
Answer: The simplest formula for calcium carbide is Fe3C.