Hi grammarians!
Can someone please tell me the latest rule regarding the use of
the last comma in a series?  Some of my grammar books say that
one must include it in formal writing, while not in informal writing
such as journalism; others say that the last comma is needed
only if misreading would occur without it, as in
 
We elected our president, vice president, secretary and
treasurer.
 
(as though the last two might be one person).
 
I'd appreciate your thoughts on this soon as I'm teaching
commas this week.
 
Carole Hamilton
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