In general, use numerals to express numbers 10 and above, and use words to express numbers zero through nine.

Example given:

students were in the third, sixth, eighth, 10th, and 12th grades

Your example does not follow the style guide and is an example of when to use digits

Percentages 50% 75%–80%

If you’re a professional writer, you should be following the style guide and this is explicitly spelled out by the APA.

apastyle.apa.org/…/numerals