The number of’… is followed by a singular verb.
When we use ‘the number’ we refer to a specific number.
The number of seats reserved is 150.
‘A number of’… is used with a plural verb.
When we use ‘a number of‘ we mean ‘several’ or ‘more than one’, so a plural verb is used.
Example: A number of passengers were injured.
|The number of online customers is increasing.
|A number of customers are complaining about slow delivery.
|The number of passengers is limited to 50.
|A number of people are waiting for the bus.
|The number of contaminations is increasing.
|A number of those contaminated are in intensive care.
|The number of road accidents is causing great concern.
|A (large) number of accidents are due to careless driving.
|The number of guests at the wedding was quite small.
|A number of guests were wearing very stylish clothes.
|The number of employees needed is fifteen.
|A number of candidates were successful.
|The number of those who were successful is 37.
|A (surprising) number of candidates have applied.
|The number of unemployed people is causing alarm
|A number of social problems are caused by unemployment.
|The number of people allowed into the museum is limited.
|A number of people were refused entry into the museum.
|There are a number of new recruits this year.
|Here is the number of those who were recruited this year.
|There are a number of different options to choose from.
|The number of options proposed is considerable.