She soon realized that writing involved following certain rules and conventions, and that many of these rules and conventions were unknown to her. At least 8 or 9/eight or nine times a day, for example, she wondered if she should spell a number as a word or write it as a figure.

Not wanting to appear ignorant, she said to herself, "I’ll just do what everyone else is doing." So she started watching for patterns.

9/Nine of her colleagues, she noted, spelled out numbers as the first words in sentences, but eleven/11 did not. 13/Thirteen wrote the day’s date as November 28^th, but 7/seven wrote it as November 28. And five/5 spelled out percentages, as in twenty-five percent, but fifteen/15 wrote percentages as figures, as in 25%.

She even noted that ten/10 of her colleagues repeated spelled-out numbers in parentheses, as in "You have three (3) days to fill out these seven (7) forms for your two (2) accounts," but that ten/10 did not. She wondered if repeating the numbers might have something to do with a custom dating back to the days before typewriters.

2/Two of her colleagues spelled out dollar amounts, as in nine thousand dollars, but eighteen/18 of them wrote dollar amounts as figures, as in $9,000. Of the eighteen/18 who wrote dollar amounts as figures, thirteen/13 did not use commas in four-digit figures, as in $1000, but five/5 did, as in $1,000.

She also noted that, of the eighteen/18 colleagues who wrote dollar amounts as figures, twelve/12 included the decimal and zeroes with even dollar amounts, as in $75.00, but six/6 did not, as in $75. Of the 6/six who did not, however, 4/four did include the decimal and zeroes when the even dollar amounts appeared in a series, as in $18.13, $16.00, and $17.95. She guessed they did so for consistency.

At the end of her first week she felt frustrated and confused.

"Maybe," she thought, "if I review the 1500/1,500 email messages I received this week, the patterns will become clear to me," and so she did.

Later that day her mentor suggested she use a style manual rather than try to imitate what her colleagues were doing. (Her mentor also pointed out that the second choice in each numbers pair above was the correct choice.)

"What’s a style manual?" she asked.

"It’s a book that explains the rules," her mentor said. "If you followed seven simple rules, you would know that, in all of the examples above, the second choice is correct."

"Where can I find a style manual?" she asked.

"Click here."

"Where can I find exercises to help me practice?"

"Click here."

First, how about a little warm-up quiz? Choose the correct numbers usage in the following sentences.

"You have thirty/30 seconds to read these four sentences and make your choices."

"These four/4 rules apply to at least twelve/12 common situations."

"Four hundred/400 or more people turned out for the solstice celebration on the Stone Arch Bridge."

"Are you ready for the four/four (4) rules?"

Here they are:

1. For numbers lower than 10, use words; for numbers of 10 or higher, use figures. In other words, write numbers of two digits or more as figures (as in "30 seconds").

Note, however, that monetary amounts and percentages are written as figures, not words, even when they are lower than 10.

2. Treat all numbers in a sentence or paragraph consistently. If all the numbers are nine or lower, use words. If the largest number is 10 or higher, use figures for all the numbers.

But note two special cases:

(a) In newspapers, magazines, and other publications following Associated Press guidelines, single-digit numbers in a mixed series (that is, in a series containing some numbers of 9 or lower and some numbers of 10 or higher) do not convert to figures.

For example, in AP style, the numbers in the parenthetical phrase in the preceding sentence would appear as "nine" and "10," not as "9" and "10." In other words, the "nine" does not convert to "9."

(b) The consistency rule applies only to numbers referring to the same category. For example, the second sentence in the quiz should be written as follows: "These four rules apply to at least 12 common situations." Because the number "four" refers to "rules," not "situations," it does not convert to a figure.

But note: "I spelled 114 words correctly and 3 words incorrectly," and according to AP style, "I spelled 114 words correctly and three words incorrectly."

I know. This rule is complicated. Fortunately, the remaining rules are simple.

3. When a number is the first word of a sentence, spell it as a word even if it would normally appear as a figure, as in "Four hundred or more people turned out . . ."

If possible, however, rephrase the sentence to avoid beginning with a number, as in "At least 400 people turned out . . ."

4. Do not repeat a spelled-out number in figures. The number in the fourth sentence (and in my opening paragraph) should appear as "four," not "four (4)."

Back in the days when business documents were written in longhand, numbers were written both as words and as figures for legibility, but today it isn’t necessary. In fact, it’s silly: "You have four (4) days to fill out these three (3) forms to verify you are eighteen (18) years or older."