Copyright © 2008, Steven E. Houchin
( Originally written 14 April 2008 )
I tend to spell out most numbers in my novels (the main exception being dollars and cents). There are definite, but sometimes conflicting, rules for how to spell out numbers in a manuscript. There are several web sites that attempt to deal with this subject. One is Tina Blue's Grammar and Usage for the Non-Expert. Another is at edufind.com.
I'll try to summarize some of the points here.
1. Hyphenate compound numbers from 21 through 99. For example: sixty-five, thirty-one. But, larger numbers aren't hyphenated: one hundred fifty-six (not one-hundred-fifty-six).
2. Hyphenate fractions. For example: three-fifths, one-tenth. But, there are exceptions. If there is already a hyphen present in either the numerator or denominator, no other hyphen is added. For example: twenty-five thirty-eighths (not twenty-five-thirty-eighths). Also, no hyphen is used when the fraction is used as a noun: They were scoreless after three quarters.
3. Hyphenate numbers when joined with a unit of measurement to form an adjective. For example: twenty-five-minute walk, thirty-six-year-old man, fifty-yard pass, seventeenth-century historian. This rule also holds true when using digits: 25-minute walk. But, when not used as an adjective, the joining hyphen is not used, as in: walked twenty-five minutes (not twenty-five-minutes), passed fifty yards (not fifty-yards).
Clearly, describing these rules is quite complicated, but if we write numbers this way, it is a subject we need to understand.