Grammar: Possessive Nouns

Some Rules:

If two people own one thing, use an apostrophe for the second person only.

Ex. Ann and Rick's car (they own one car)

If two people don't own one thing, use an apostrophe for both.

Ex. Ann's and Rick's toes (they each have their own toes)

*Now, if a plural ends in s (boys) just add an apostrophe. Ex. The boys' jackets

*If the plural does not end in s (women, children) add an apostrophe and an s. Ex. The children's toys

Here's a cheatsheet:

The girl's coat= one girl, one coat
The girls' coat= two (or more) girls sharing the same coat
The girls' coats = two (or more) girls with different coats

Taken from the book Painless Grammar (Painless Series)
by Rebecca Elliott