Derive the molecular formula of a carbohydrate in which the mass fraction of carbon is 40%,

Derive the molecular formula of a carbohydrate in which the mass fraction of carbon is 40%, hydrogen-6.7%, oxygen-53.3%.

Let us denote: x is the number of carbon atoms, y is the number of hydrogen atoms, z is the number of oxygen atoms, M is the relative molecular weight of the substance.
The relative atomic mass of carbon is 12, oxygen is 16, and hydrogen is 1.
Let’s compose the following expressions:
0.4 = 12 * x / M;

0.067 = 1 * y / M;

0.533 = 16 * z / M;

Let us express the molecular weight from the expressions:
M = 12x / 0.4 = 30x;

M = y / 0.067 = 15y;

M = 16z / 0.533 = 30z;

Let’s equate the obtained expressions: 30x = 15y = 30z. This substance is formaldehyde, its formula is CH2O.
Answer: the formula of the substance is CH2O.