In each of the following sentences, a connective symbol is employed in a reference to numbers or numerical values, but the usage is incorrect. Explanation of the error, and a revision of the error, follows each example.
1. Open enrollment for 2018 runs from November 1 – December 15.
A connective symbol linking two values in a number range functions as a replacement for from and to (or between and and), not just the latter word (though only to is pronounced when the number range is read aloud, hence the confusion), so do not precede a number range formatted this way with from (or between): “Open enrollment for 2018 runs November 1–December 15.” If the word from is retained, to should replace the symbol. (Note also that the symbol should be an en dash, not a simple hyphen—except when a publication’s style guide specifies use of that symbol—and that no letter spaces should intervene.)
2. Five-thousand service members are expected to participate in the event.
Hyphenation is used in spelled-out numbers only to link two words representing two place values, as in seventy-five. “Five thousand” modifies “service members” but is an open compound: “Five thousand service members are expected to participate in the event.”
Note that large round numbers are often spelled out in isolation but should be treated as figures if other numbers appear in proximity, but numbers should always be spelled out at the head of a sentence. (If doing so is awkward, as in the case of a large precise number such as that representing a year like 2017 that requires more than a couple of words to convey, recast the sentence.)
3. The most fatalities occurred in the 15-24 year old age group.
In most books and in some publications, style would dictate that the numbers in this sentence should be spelled out. However, in other content, or in a case in which using numerals is preferable (as when a concentration of numbers occurs), the phrase in which the figures appear should be treated as shown here: “The most fatalities occurred in the 15- to 24-year-old age group.” (When numbers are spelled out, the sentence should read, “The most fatalities occurred in the fifteen- to twenty-four-year-old age group.”)
The hyphen does not function as a linking symbol connecting two figures in a number range; it links words that are part of a phrasal adjective, an abridgement of “15-year-old to 24-year-old” in which the first instance of “year-old” is omitted because it is clearly implicit. (This tactic, called suspensive hyphenation, renders such phrases more concise and less cluttered. In addition, the sentence can be further pared to “The most fatalities occurred among 15- to 24-year-olds.”)