**1. The problem statement, all variables and given/known data**

This is a question from a chemistry book

Two oxides of a metal contain 27.6% and 30% of oxygen respectively. If the formula of the first oxide is MO, find that of the second?

3. The attempt at a solution

3. The attempt at a solution

In the first MO, if the total amount is 100g, then O is 27.6g similarly,

in the second MO, if the total amount is 100g, then O is 30g respectively

1.725 mole of O is 27.6g.

in the MO, 72.4g of M left.

But my question is how to calculate the mole of M? because I don't know the molar mass of M