These three sentences exemplify incorrect insertion or omission of hyphens in numerical references. Each sentence is accompanied by a discussion and a revision.
1. The two albums have sold close to 30-million copies combined worldwide.
The combination of a numeral and a word expressing an order of magnitude is never hyphenated; the usage, a simplified version of the cluttered-looking numerical representation 3,000,000, is not a phrasal adjective: “The two albums have sold close to 30 million copies combined worldwide.” (This is true even when the number is a phrasal adjective: “The 30 million figure is unprecedented,” though it is better to relax such a statement to read, “The figure of 30 million is unprecedented.”) “The 30-million-dollar figure is unprecedented.”
In such usage, the number is often spelled out: “The two albums have sold close to thirty million copies combined worldwide.” No hyphen is required in this case, either (“The thirty million figure is unprecedented”), though, again, it reads better in a more relaxed state (“The figure of thirty million is unprecedented”).
When yet another word is included to form a phrasal adjective, however, whether the number is in numeral form or spelled out, hyphenate all three elements: “The 30-million-dollar figure is unprecedented”; “The thirty-million-dollar figure is unprecedented.”
2. These phases are often subdivided into 30, 60, and 90-day segments to manage specific milestones with greater precision.
This sentence refers to segments of 30, 60, and 90 days’ duration, but the word day in the phrasal adjectives “30-day” and “60-day” has been elided because the use of the word in “90-day” makes it clear that the unit of time is implied for all three numbers. However, when this technique, called suspensive hyphenation, is employed, the hyphen must be retained after all three figures: “These phases are often subdivided into 30-, 60-, and 90-day segments to manage specific milestones with greater precision.”
3. We anticipate that significant unplanned outages of the network will occur approximately five-ten times a year.
If the numbers in this sentence were treated as numerals, the correct style would be “5–10 times a year,” but an en dash should not be used in a number range when the numbers are spelled out (nor should a hyphen, which, as here, is often used erroneously in place of the dash): “We anticipate that significant unplanned outages of the network will occur approximately five to ten times a year.” (Some publications deliberately use hyphens in number ranges because a hyphen takes only a single keystroke to type.)
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