Dear GB:

You wrote:
> If referring to multiplication tables i.e.: fives times tables etc., do you use an apostrophe if you contract it to – 5s 6s 7s etc or write it as 5’s, 6’s 7’s etc.?
>
> Also, a family name as in my case Blank, [not the real name] is an apostrophe used when
talking collectively about the Blank family (the Blanks or the Blank’s) and so on?
>
These are good questions. In the first case, you do see authorities do it both ways. The first way is considered standard; it is simply the plural of the number. However, especially in mathematical situations, you do sometimes see 5’s (“fives”) to distinguish the plural of five from the algebraic expression 5s (i.e., five times s). Neither is really appropriate in any
formal writing. In any formal writing, write out the word so there is no ambiguity: “fives, sixes, sevens, etc.”

In the second case, the apostrophe is only used with the possessive. So you would normally say “the Blanks,” i.e., the Blank family. The only time you would use the apostrophe would be if you were using it with the possessive:
“George Blank’s brother” or “the Blanks’ house.”

I hope this helps.