Q. In a large document, I am spelling out numbers under 100. For consistency, if I have a sentence with a list that includes 99 and 101, I would write them both as numerals. Does this rule apply per sentence, per paragraph, per page, per report? This feels like such a silly question, but I honestly am struggling with it.

Q. I see the word “that” in constructions where clarity would not be diminished without it. An example in the Q&A was “He thinks that, if he asks for directions, his membership in the brotherhood of men will be revoked.” I consider “He thinks if he . . .” correct.

Q. If I’m expressing a range of percentages in a statistics-heavy paragraph of academic social sciences prose, does the percent sign commute? For example, does “50 to 55% of respondents” make sense, or should I use a percent sign after each numeral, making it “50% to 55%” instead? What about other units of measurement? Is “from 100 to 110km” better or worse than “from 100km to 110km”?

Q. A colleague writes: “Basement space is about 5,700 square feet, but about 12,000 square feet is available on the eighth floor.” I suspect the point is arguable, but couldn’t that be “12,000 square feet are available on the eighth floor”?

Q. What is the correct way to report ages of people? In what cases, if any, would it be acceptable to use numerals? Our company’s style guide follows CMOS, but suggests using figures in reporting ages. I appreciate your guidance.

Q. Hi. Is it acceptable to begin a sentence with a mathematical variable? I had been going by the thinking that since one spells out a number when beginning a sentence, one would not begin a sentence with a variable or other mathematical expression. However, I have seen numerous such occurrences in journal articles, leading me to think that copy editors would have made corrections if this were considered a stylistic error. I have not been able to find any advice about this, and so I was wondering about your stance on it. Thank you.

Q. Hi, CMOS people, I can’t quite seem to figure out whether I should use spelled-out numbers or numerals with units of time—for example, seconds, minutes, hours, days, months, years. I am not sure whether it should be “2 to 4 weeks” or “two to four weeks”; “30 years” or “thirty years”; etc. I think for numbers over 99, numerals are used, for example “230 seconds.” I understand that numerals should be used with units of measure in general, like kg, cm, °C, and °F, etc. Thank you for your help.

Q. Section 9.38 seems pretty straightforward: “Times of day in even, half, and quarter hours are usually spelled out in text.” I’m an editor on contract with one of the larger self-publishing companies. I recently got this note from an editorial staffer: “In several instances, you changed references like 1:00 a.m. and 10:00 p.m. to one a.m. and ten p.m. . . . If you have found specific Chicago rules to support the changes you’ve made, please let me know and I’ll be happy to pass the manuscript through as is. However, I don’t know of a rule that would allow that. If you don’t know of one either, would you please change the time references with a.m. and p.m. back to numeral form and resend?” For seven years, I’ve been spelling out times of day ending with :00, :15, :30, and :45, with or without a.m./p.m., if they did not seem particularly significant in context. This is the first time it has been called into question.

Q. Is it correct to say $3–5 million? Or should it be $3 to $5 million? Or $3 million to $5 million?

Q. I am taking a college course in copyediting. My professor and I were having a discussion and I would like to know who is correct. We were presented with this sentence for correction: Of the 400 members, about 300 were over 60 years old, but at least 50 were under the age of 30. I understand the rules stated in 9.2 and 9.4 would apply here and require all of the numbers to be spelled out. However, I chose to leave the 60 and 30 in numerical form in accordance with 9.7, “To avoid a thickly clustered group of spelled-out numbers, numerals may be used instead in exception to the general rule.” There are no guidelines that state when to apply the exception, nor are there examples to lead me to a definitive answer. Help please. How do you decide?