"Alice bought 12 apples, 1 banana and 6 cantaloupes": Should the numbers be written with letters or digits?

Question

I want to write a sentence with a similar structure as follows:

Alice bought 12 apples, 1 banana and 6 cantaloupes.

Should the numbers be written with letters or digits? The sentence is just an example, I'm interested for any context, e.g. in academic writing.

I believe that typically integers strictly smaller than 10 should be written with letters while integers strictly greater than 9 should be written with letters, but in this case that would result in a mix of letter and digits, which don't seem consistent within the sentence.

Answer 1

Go with whatever looks right to you. There's nothing wrong with using numerals in this context. The rule to use words for numbers under ten is just a guideline (and I've seen the rule as "numbers under thirteen")

I agree that a mixture would look odd (not wrong, but an odd stylistic choice) But both numerals or words would be acceptable here.

The genre might affect your choice. In a scientific paper, numerals might be better, in a poem, I'd use words.

Answer 2

As James K's answer states, it depends on the writing guideline. I'll some examples and sources in this answer:

From https://getproofed.com/writing-tips/everything-you-need-to-know-about-numbers-in-ap-style/ (mirror):

AP style allows you to mix words and numerals in the same sentence, so the correct version would be "Alice bought 12 apples, one banana and six cantaloupes." Other style guides suggest maintaining consistency within a sentence or paragraph where possible (i.e., using all words or all numerals for numbers of a similar type, depending on which is more appropriate and the specific style guide in question). As you mention academic writing, it may be worth checking which style guide your school recommends, since AP style is usually more common in business and journalistic writing.

NAU editorial style guide (mirror) states:

If a sentence includes multiple numbers that apply to the same thing or category, and if one of the numbers requires a numeral (10 or greater), use numerals for all the quantities of that category.