What is the correct way to write a fractional number in a formal letter?

Question

If I'm talking about a length of time in a cover letter, let's say 5.5 years, what would be the correct way to write this?

• five-and-a-half years
• 5-1/2 years
• 5.5 years

Answer 1

five and a half years

No hyphens. Hyphens are for adjective phrases:

It was a five-and-a-half-year journey.

You also don't use the hyphen with the fraction.

5¹⁄₂ years