Plurals of Numbers and Numbers That Begin A Sentence

Plurals of numbers:

My style guide indicates that the plural of a number is expressed as a figure by adding a lowercase -s:

before the 1950s
temperatures will be well into the 90s
the 5s represent nickels


Numbers that begin a sentence should be written out:


Thirty-five appointments had to be rescheduled.
Nine years ago, we opened our doors for business.
One inch margins are desired for this publication.

(NOTE: Even though "one" is followed by a unit of measure in the last example, it is spelled out, because it begins a sentence.)