Do use apostrophes with certain numbers
Now we come to numbers. You generally shouldn’t add an apostrophe to the end of a number – so you met a woman in her 50s (not 50’s) when the temperatures were in the 80s (not 80’s). In discussing dates, we generally still don’t add an apostrophe s to the end (“Bellbottoms were big in the 1960s”), whereas we do add an apostrophe at the beginning if the date is abbreviated (“But no model would be caught dead in those flared jeans by the ’90s”).
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