Grammar in Action - Number Rules

When using numbers to describe the same category in a sentence, be consistent with spelling the number out or using figures.

This number rule can often create confusion because you have to look back into the sentence to make sure all the similar categories in a sentence follow the same method of listing numbers, whether it be figures or written out. For more information on number rules, you can look here.

They're not used for 15 years, but I think they're typically for 5 or 7 years or something similar.

It is only supposed to reach 8 degrees Fahrenheit today, but the three-day high may get up to 15 degrees Fahrenheit.

Notice in the second example both instances where degrees of temperature were concerned needed to be in figure format, while the number that was discussing the number of days followed regular number rules and was written out.