The traditional rule says that you should use fewer for things that can be counted (fewer than four players) but less with mass terms for things of measurable extent (less paper, less than a gallon of paint). But people use less in certain constructions where fewer would occur if the rule were being followed. You can use less than before a plural noun that denotes a measure of time, amount, or distance: less than three weeks, less than $400, less than 50 miles. You can sometimes use less with plural nouns in the expressions no less than and or less. Thus you can say No less than 30 of his colleagues signed the letter and Give your reasons in 25 words or less.    1