Commonly Confused Words:  fewer / less

Fewer is always an adjective. 

Use fewer  to refer to countable items such as pencils, adults, trees, and computers.

   Example

Less can be an adjective or an adverb.

As an adjective, use less ONLY to refer to uncountable items such as ink, sugar, sand, and air.

   Example

Note the difference:

Link to exercises on fewer / less.