Should I write out the numbers in my essay? I have the number 15 (currently I wrote it out as fifteen) and the word 15-year-old. Should I re-write this as fifteen-year-old as well? Or both as numbers?
Generally, numbers up to 10 are spelled out, and those 10 and higher use digits. The phrase 15-year-old is correct if you use a noun after, such as “15-year-old student,” but if there is no noun, then delete the hyphens. Either way, use digits and don’t spell out the number. These are the rules according to the AP Style Book.