Arguments on the Apostrophe "s"
The grammar section was of most interest to us. I present you with question #50:
How are letters and figures made plural?
The answer is: "By annexing 's.
Since this was something I have been doing for years, it made sense. However, after a brief discussion with Craig, I realized that this use of the 's is considered incorrect and always has been in many circles. I refer you to The Green Grocer's Apostrophe, which has been abused for so long that many people don't realize it is incorrect. It's seen more in the UK than here, though not exclusively.
So, we know we don't use the 's in reference to a plural, but its use has been sanctioned in the case of numbers for many years. Or it used to be. Looked at objectively, it really is just plain wrong.