Many readers have asked me why people write numbers this way:
Example: We will need 220 (two hundred twenty) chairs.
Isn’t it unnecessary to have both numerals and words for the same number?
Rule of Thumb: There are two reasons for using both: 1. You are more likely to make an error when typing a numeral than when typing a word AND much less likely to spot the error when proofreading. 2. If your document is dense, has a lot of numbers, or contains large numbers, the numerical form helps your readers scan information quickly.
So by typing a combination of a numeral and a word, you are almost guaranteed accuracy and ease of reading.
Rule: Some authorities say that the numbers one through nine or ten should be spelled out and figures used for higher numbers. Other authorities spell out one through one hundred, plus even hundreds, thousands, and so on. The best strategy is to be consistent.
Correct Examples: I want five copies, not ten copies. I want 5 copies, not 10 copies.
Rule: Be consistent within a category. For example, if you choose numerals because one of the numbers you must deal with is greater than ten, you should use numerals for everything in that category. If you use numbers in different categories, use figures for one category and words for the other.
Correct Example: Given the budget constraints, if all 30 history students attend the four plays, then the 7 math students will be able to attend only two plays.
(Students are represented with figures; plays are represented with words.)
Incorrect Example: I asked for five pencils, not 50.