Average Molecular Mass of ozonised oxygen is 36. Calculate percentage of oxygen in ozonised oxygen

The average molecular mass of a mixture of two gasses ideally is, the sum of the product of the respective molecular masses and their mole fraction.
Let x be the mole fraction of oxygen in the mixture.
Molecular mass of oxygen is 32.
Molecular mass of ozone is 48.
Let x be the mole fraction of oxygen.
Hence, x*32 + (1-x)*48 = 36
Solving the above equation we get that x = 0.75.
Therefore the percentage of oxygen in the mixture is 75.