less or fewer?
When you’re in the supermarket, do you count your purchases to see whether you can use the register for “Less than 14 items”? I hope not. I hope your supermarket has a register for “Fewer than 14 items.” Use fewer to compare numbers of items that can be counted individually (when talking about units of time or money, however, there are some exceptions). Use less for things considered in groups or as a mass, to express degree, extent, or amount. Less also modifies adjectives and adverbs.

• We did the job in less time. (“time” is not items that can be counted individually)
• We did the job in fewer hours. (“hours” can be counted)
• The company hired fewer employees last year.
• At that store you have fewer choices and less room to move around, there are fewer salespeople, and they are less attentive. (here, “choices” and “salespeople” can be counted; “room” cannot be counted as individual items; “attentive” is an adjective modified by “less” used as an adverb).
• There were fewer than 52 cards in the deck.
• The store made less money this month than it did in April.
• but: She had less than 10 dollars. (exception for units of money)

number or amount?
These two are comparable to “less” and “fewer.” Use number in reference to items that can be counted; amount when speaking of groups as a whole or one item that cannot be counted.

• A number of employees complained about the new policy. (i.e., several employees)
• There is a huge amount of sugar in cola.
• A small number of people win the lottery every year.

a number is, or a number are?
Related to “a number” is the question of whether it should be followed by a singular or plural verb. In the example of the employees, above, “a number [of employees]” seems to imply a singular verb, since “a” means “one.” Would it be correct to say “a number of employees is going to the retirement luncheon”? “A number of,” “a diversity of,” “a variety of,” and similar constructions are idiomatic expressions that mean “several” or “many” or “a few.”

The rule is very simple: An expression such as “a number (total, variety, diversity) of” that means “several,” “many,” or “a few” is followed by a plural verb. If you can substitute “several” in your sentence, use a plural verb. “The number (total, variety, diversity) of” is followed by a singular verb. “The number” is referring to a single entity.

• A number of experiments have supported our results. (“several experiments” or “a few experiments”)
• The number of experiments in this area has greatly increased in the last few years. (whatever that number is, it is larger now. The sentence is referring to a single body of experiments).
• A diversity of students now enjoy the benefits of this program. (“several or many different ethnicities of students”)
• The diversity of students at this school is surprising. (the single issue of diversity)
• A variety of viewpoints were heard during the meeting. (“many different viewpoints”)
• The variety of viewpoints heard during the meeting was not expected. (the fact of a body of viewpoints)
• A total of 120 tests were conducted
• The total is 120.

Notice that “a number of” is not comparable to collective nouns such as “group” or “team.” It would be incorrect to say “a group of foreign visitors are coming in for a tour.” “A group” is a single entity. The word “several” cannot be substituted for “a group of” because “several visitors” would mean separate, independent visitors, not members of a single group.

• A group of foreign visitors is coming in for a tour.
• The group of foreign visitors is having lunch at The Outback restaurant.