A number represents an amount that can be counted. The word "number" can be used as a noun or as a verb.
The crowd numbered in the thousands.
The teacher told the students to number their sentences.
Players on a football field are numbered so that fans can pick them out more easily. (pick them out = identify them)
I can number several good reasons for eating a healthy breakfast in the morning.
The word "number" is often used in front of a number when speaking about it directly.
The number four is evenly divisible by two.
The number three is not evenly divisible by two.
Five is Joe’s lucky number.
The number seven is regarded as lucky.
The number 13 is regarded as being unlucky.
Tom Brady wears number 12 on his jersey.
The word "number" is often used in the form of a plural when talking about amounts of things that are significant.
The doctor told me to pay attention to the numbers on my health chart.
Our numbers are increasing at the school. (We’re gaining students.)
Quarterly numbers indicate that the company made a good profit.
The numbers we’re using show that profitability is possible within two years.
The numbers in this budget proposal just don’t add up.
Notice that there is a difference between "a number" and "the number."
A number of people are interested in this subject. ("A number" is a plural subject in this sentence. We don’t know what the number is, but we know it’s greater than one.)
The number of people interested in this subect is increasing. ("The number" is a singular subject in this sentence. Here we are thinking of one number.)
The police arrested a number of people who were protesting in the street.
The number of people arrested was reported in the newspaper.
A number of people called to complain about the noise coming from the building. The city received about 30 calls.
This writing assignment has a number of mistakes on it. (This sounds like a lot of mistakes!)
