Are you puzzled about the rules for numbers? If you are, you are not alone. People, organizations, and grammar and style books all seem to have their own preferences.
British English recommends writing out all numbers under 100, but, according to The Canadian Press Stylebook, you should use words for numbers between one and nine. Use the figures for 10 and up.
If you are presenting a string of numbers above and below 10, keep to the rules.
Example (Canadian style)
There will be 20 people attending the board meeting: 11 official members, three staff members, and six ex officio members.
The Chicago Manual of Style disagrees and says not to mix numerals and written numbers when referencing similar things.
Example (American style)
There will be 20 people attending the board meeting: 11 official members, 3 staff members, and 6 ex officio members.
Fortunately, both style books agree there are occasions when you should ignore the over-and-under-10 rule. Use figures when mentioning:
A. Scores, percentages, votes, odds, dates, years, addresses, and in money amounts
preceded by a symbol ($5) and in times (8 o’clock, 11:45 a.m.)
B. Use figures in lists of instructions and when trying to save space in a headline.
C. Use words when starting a sentence and when using numbers loosely.
Fifty to 60 people attended the annual general meeting. Thousands of people were left homeless after the earthquake and hundreds were injured.
In business writing, you would never present numbers both ways. Incorrect: He attended eight (8) meetings.
In North American emails, there is a trend to always use figures for numbers. Although it may be considered a substandard style by purists today, I believe it will become acceptable within the next few years.