The mass fractions of carbon, hydrogen and nitrogen in the tertiary amine are equal

The mass fractions of carbon, hydrogen and nitrogen in the tertiary amine are equal to 65.75%, 15.07%, 19.18%, respectively. Derive the amine formula.

Let us denote: a is the number of carbon atoms, b is the number of hydrogen atoms, c is the number of nitrogen atoms, Mr is the molecular weight of the compound.
The relative atomic masses of the elements are known: carbon is 12, hydrogen is 1, nitrogen is 14.
Let’s compose the following expressions:
0.6575 = 12a / Mr;

0.1507 = b / Mr;

0.1918 = 14c / Mr;

Let’s express the molecular weight:
Mr = 12a / 0.6575 = 18.25a;

Mr = b / 0.1507 = 6.6357b;

Mr = 14c / 0.1918 = 73c;

Let’s equate the expressions: 18.25a = 6.6357b = 73c. Unknown values are equal: a = 4, b = 11, c = 1.

Answer: Amine formula: – C4H11N (diethylamine).