Generally, people should write numbers out the way they sound. For example, 2,345 could be written as "two thousand three hundred forty-five." When writing numbers out for a check, hyphenate numbers between 21 and 99. Although style books offer different rules, consistency on the writer's part is key.
On a check, write the full dollar amount and use a fraction for cents. For example, write "three hundred sixty-two dollars and 47/100" for $362.47. There is no need to write "point four seven dollars." Avoid writing informal phrases such as "sixteen hundred" on a check; write "one thousand six hundred" instead.
The Associated Press Stylebook recommends writing numbers one through nine as words and using digits for anything greater than 10. However, the Chicago Manual of Style recommends writing numbers one through 99 in full. As policies differ between publications, it is up to the writer to be consistent.
If a number starts a sentence, it should be written in full, although it is acceptable to start a sentence with a year written numerically. Hyphenate fractions such as "two-thirds," as well as numbers between 21 and 99.
Numbers representing decades do not need to be capitalized; "the eighties" is preferable to "the Eighties."