“There are people who cringe at the grocery store when they see the sign '10 items or less,'” said Anne Curzan, a professor of English at the University of Michigan.
It seems as though the rule for less vs. fewer is becoming less clear.
She said, “The rule is that with nouns that are countable we should use fewer. And with nouns that we can’t count, such as water, we should use less.
“Ten items, clearly you can count them because there are ten, so it should be fewer. If you have money it would be less money, but fewer dollars.”
The principles are the same with amount vs. number, so amount for an uncountable noun, and number for a countable noun.