- When do you use hyphens in numbers?
Incorrect: There are three-hundred-sixty-five days in a year.
Correct: There are three hundred sixty-five days in a year.
Use a hyphen when writing out the numbers twenty-one to ninety-nine in words. Do not use hyphens for other numbers.
Incorrect: France has a 35 hour working week.
Correct: France has a 35-hour working week.
Incorrect: The ten year old boy wanted to become an archaeologist.
Correct: The ten-year-old boy wanted to become an archaeologist.
Use hyphens only when the number functions as an adjective phrase.