Dear Slithy Toves,

And that rule for apostrophes for plurals of numbers and letters is the one that I thought I'd heard somewhere along the way.

So, where does that leave us with R's catigation of the students for 1800s v. 1800's? Are dates considered to be numbers different from numbers functioning simply as numbers? And then musical beats would definitely be groups in sets of 2's and 3's according to the site you provided. But what about when you spell 'em out? Does the apostrophe number rule still apply? Beats in sets of two's and three's?

Still wondering,
WW