The combination of numbers, spelled out or in numerical form, and hyphens is a volatile mixture that often confuses writers. Here are five sentences in which hyphens are erroneously inserted into constructions that do not require them, with explanations and corrections.
1. “Four-percent of adults may have ADHD.”
There’s no reason to combine four and percent. The writer might have incorrectly extrapolated from the use of fractions in the same type of construction (“One-third of respondents agree with the statement”), but the sentence should read, “Four percent of adults may have ADHD.”
2. “Astronomers say an object five-times bigger than Jupiter is the first planet outside our solar system to be imaged.”
The reference to the exoplanet’s magnitude of size in comparison to Jupiter requires no linking hyphen. The misunderstanding perhaps arises from the fact that “five times” modifies bigger, but bigger is an adjective, not a noun, and words combining to modify adjectives are not hyphenated. The correct form is “Astronomers say an object five times bigger than Jupiter is the first planet outside our solar system to be imaged.”
3. “This monk began his vow not to speak with a 2-1/2 year walk up the coast.”
Writers often erroneously insert a hyphen between a whole number and a fraction in a mixed fraction. It’s not necessary, but it is required between the mixed fraction and the noun that follows when they combine to modify another noun, as in this example: “This monk began his vow not to speak by taking a 2 1/2-year walk up the coast.” (2 1/2 is considered a single element, so omit the intervening hyphen.) Note, too, the slight revision to eliminate the suggestion that the monk conversed with a 2 1/2-year walk up the coast.
4. “The electrified border, 10-feet-high, is to be completed across the border with India.”
If this sentence used the phrase “10 feet high” as a modifier preceding “electrified fence” (“a 10-foot-high electrified fence”), the hyphens linking the elements as a unified description would be valid. But in a simple reference to physical dimensions, no hyphens are necessary: “The electrified fence, 10 feet high, is to be completed across the border with India.”
5. “You must have a keen sense of how to capture the attention of the 18-34 year-old news junkie.”
This sentence tries to observe the basic rule about connecting the numbers in a range (preferably with an en dash rather than a hyphen) but errs in its failure to recognize the special case of suspensive hyphenation that overrules that usage. The sentence refers to a demographic cohort consisting of 18-year-old news junkies and 34-year-old news junkies and all news junkies in between. When using a range involving a number compound, elide most of the first element, retaining only the number (spelled out or in numeral form) and a hyphen, followed by a letter space: “You must have a keen sense of how to capture the attention of the 18- to 34-year-old news junkie.”