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.

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.

Both options A and B are correct, but they differ in terms of punctuation and meaning. Let's break it down:

A) The personnel director, Ms. Smith, hired three typists and two case managers.
In this option, the sentence is structured with commas to set off the appositive phrase "Ms. Smith" from the rest of the sentence. This gives additional information about who the personnel director is. The sentence states that the personnel director, who is identified as Ms. Smith, hired three typists and two case managers.

B) The personnel director, Ms. Smith, hired three typists, and two case managers.
In this option, the sentence also has commas to set off the appositive phrase "Ms. Smith" from the rest of the sentence. However, there is an additional comma before the word "and," which is called a serial comma or Oxford comma. This comma is optional and is used before the coordinating conjunction "and" in a series of three or more items. As a result, this option indicates that the personnel director hired three typists, and separately, two case managers.

Both options can be correct, but their meaning slightly differs due to the use of the Oxford comma in option B. It's important to note that the use of the Oxford comma can vary depending on the style guide or regional conventions.