19.2.4 Accepted Usage.

Spell out numbers for generally accepted usage, such as idiomatic expressions. One frequently appears in running text without referring to a quantity per se and may appear awkward if expressed as a numeral. When one may be replaced by a or a single without changing the meaning, the word one rather than the numeral is usually appropriate. Other numbers, most often zero, two, and large rounded numbers, also may be written as words in circumstances in which use of the numeral would place an unintended emphasis on a precise quantity or would be confusing.Any one of the 12 individuals might ...Less