# Difference between Oxidation Number and Oxidation State [duplicate]

I know the theoretical definitions and that they do not defer much, infact these terms are used quite interchangeably.

However, my chemistry teacher once taught me that Oxidation State of an atom in a compound is the average of the different Oxidation Numbers in the molecule. For example, in Acetic acid, the Carbon atom has oxidation numbers +3 and -3, so the Oxidation State of Carbon (i.e. the average) would be 0.

I've stuck by this for long, but yesterday I came across a question the answer to which implies that it is the other way round, as in ON is actually the average of all the OS of an atom. Several sites on the internet quote the same, and other references quote what my teacher taught me, which is the opposite.