fewer and less

Fewer is the comparative of few (used before plural nouns)
Less is the comparative of little (used before uncountable nouns which are singular)

• few problems/ fewer problems


• little money/ less money


• I've got fewer problems than I used to have


• I earn less money than a postman.

In informal English, some people use less with plural words

• I've got less problems than I used to have.