A number word placed in front of a noun acts like an adjective. The number word modifies the noun by telling how many there are.
Here are some sentences using a number word with a noun to tell how many. These number words are
adjectives.
My neighbor has three poodles.
I read two books over my winter break.
This cake recipe calls for four eggs.
In each of these sentences, a number word modifies a noun by telling how many there are.
three poodles – two books – four eggs
Ordinal numbers also act as adjectives. Look at these sentences:
My brother is in the fifth grade.
I tripped on my third lap around the track.
The first book I ever owned was given to me by my dad.
The adjective fifth modifies the noun grade.
The adjective third modifies the noun lap.
The adjective first modifies the noun book.
Number words act as adjectives when they are placed right before a noun. The adjective modifies the noun by telling how many.