Form 4 Chemistry

Question

The relative atomic mass of element X is 74.9. It forms an oxide containing 24.3% of oxygen by mass. What is the mole ratio of X to oxygen in the oxide?

[Steps please]

I've checked the periodic table. FYI, element X is As (atomic no. 33).

Answer 1

In 100 g of the oxide of X,
Mass of X = 100 – 24.3 g = 75.7 g
Mass of O = 24.3 g

Since no. of moles = mass / (molar mass)
Mole ratio X : O = 75.7/74.9 : 24.3/16 = 1.01 : 1.52 = 2 : 3