Number words are adjectives. Every time you put a number word with a noun, you are using an adjective.
I bought two ears of corn at the market.
We need five potatoes for dinner.
Bobby read twenty books during the summer.
My neighbor has three noisy dogs.
A number word modifies the noun when placed in front of the noun. That makes the number word an adjective.
Now you try it. Find the number word adjective in this sentence. I brought three cookies in my lunch so I can share with you. That wasn’t too hard, was it?