What is the ratio by mass of constituting elements in calcium oxide?

The ratio by mass of constituting elements in calcium oxide is 5:2.
As we know,
The chemical formula of calcium oxide is CaO
Mass of calcium atom = 40g
Mass of oxygen atoms = 16 g
Ratio by mass is the ratio of masses of two elements in a compound.
The ratio of calcium and oxygen in CaO  = Ca:O
                                                                      $\Rightarrow$ $40:16$
                                                                      $\Rightarrow$ $5:2$