The sentence - "The 2 and a half story house was burnt to the ground." - does AP style reccommend spelling out 2 1/2 or simply using the numerical form? Thanks
Search with the Google

engine over the AP site by searching for:
site:www.ap.org "two and a half"
site:www.ap.org "2 and a half"

You'll get stuff such as:
"for mixed number 1 1/2, 2 5/8, etc., with a full space between the numeral and the fraction"
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I don't know if it's different when used with "and a half," but AP style for numbers is you spell out one through nine and use numerals for 10 and greater.
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Just checked and Grammar Geek is correct. In this case it should be 2 1/2.