Question

writing punctuation: The personnel director Ms Smith hired three new typists two case managers

A) The personnel director, Ms. Smith, hired three typists and two case managers.
B) The personnel director, Ms. Smith, hired three typists, and two case managers.

Answer 1

The correct sentence depends upon the style guide you're using. There is no universal decision about what is called the Oxford comma.

http://www.oxforddictionaries.com/us/words/what-is-the-oxford-comma

As a journalism student, I was taught not to use it because it was just one more key stroke for the type setter.