For me average is - educationally - wrong.
Putting aside question whether to use oxidation numbers or not, as the debates are hot (and there are more arguments against, then for), if you decide to use them they are defined as the charge of the atom in the compound.
So first you are explaining to your students that charge is integer and can't be divided, then you make them calculate oxidation number of Fe in Fe3
No better way of creating confusion as giving contradicting information through the reliable sources (which loose their credibility in the process).
That reliable source is a teacher in case you missed that one
No wonder some students hate chemistry.Edit/sidenote:
such problems are one of the reasons to NOT use oxidation numbers at all.