Here's why:
* Adjective: When a numeral describes or modifies a noun, it acts as an adjective.
* Example: "There are three apples on the table." (Three describes the number of apples)
* Noun: When a numeral stands alone and refers to a quantity or number, it acts as a noun.
* Example: "I need two." (Two refers to the quantity needed)
It's important to remember that numerals are not verbs, adverbs, or pronouns.