Good and Bad Writing -- Exercises in Evaluating Writing Samples
Mechanics -- Numbers
In general numbers less than three digits should be spelled out while Arabic numerals should be used for numbers of three digits or more.
A sentence should never begin with a numeral. Numbers must be spelled out if they come at the beginning of a sentence. It is best to change the sentence so it does not start with a number at all.
When used in a series, numerals should be used for all numbers.
The army suffered 200 dead, 34 wounded, and 9 missing.
For large round numbers, spell them out.
seven million records sold 3.4 million records sold
three hundred million
When writing percentages, use numerals (unless it begins a sentence) and the word “percent.”
The stock increased 20 percent. Twenty percent of the army was killed.