Less is the comparative of little. It is used before uncountable nouns.

Fewer is the comparative of few. It is used before plural nouns.

• Fewer than ten students participated in the program.
• We did less work today than yesterday.

Notes

In informal English, less is often used before plural nouns.

• No fewer than fifty miners were killed in the explosion. OR No less than fifty miners were killed in the explosion.

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1. Less and Fewer