Number Noun Adjectives
Rule 2.3: Do not pluralize number-noun adjectives that precede a singular, countable noun
He won the world championship twenty times.
Correct: He’s a twenty-time world champion boxer.
Incorrect: He’s twenty-times world champion boxer.
She’s a girl who is seven years old.
Correct: She’s a seven-year old girl.
Incorrect: She’s seven years old girl.
