Rule 1

A number of my friends (is / are) moving to a new city.

• is

• are

The number of books in the library (is / are) over 500,000.

• is

• are

A number of errors (was / were) found in the report.

• was

• were

The number of registered voters (has / have) gone down this year.

• has

• have

A number of old buildings (was / were) demolished last week.

• was

• were

The number of accidents on this highway (is / are) worrying.

• is

• are

A number of talented musicians (performs / perform) at the festival every summer.

• performs

• perform

The number of species becoming extinct (grows / grow) annually.

• grows

• grow

A number of new video games (comes / come) out every month.

• comes

• come

The number of people who own smartphones (exceeds / exceed) 3 billion.

• exceeds

• exceed