Quote:
Usage: The comparative of few, fewer, properly refers to a countable quantity: Express checkout is for 10 items or fewer. Formally, less is confined to uncountable, mass quantities: less salt; fewer people; less water; fewer potatoes; less time and trouble; fewer problems. People rarely use fewer for less, but often use less where fewer is preferred (10 items or less), a usage frowned upon by purists.
Here is a worksheet that has many different count and noncount nouns:
