Though, a common rule is that cardinal numbers one through nine should be spelled out in an essay or article, while numbers 10 and above be written in figures. An alternative rule is to spell out numbers of one or two words (such as two and two million), and use figures for numbers that require more than two words to spell out (such as 214 and 1,412).
In either case, numbers that begin a sentence should be written out as words.
Regardless of which rule you choose to follow, exceptions are made for dates, decimals, fractions, percentages, scores, exact sums of money, and pages – all of which are generally written in figures. In business writing and technical writing, figures are used in nearly all cases. Some examples are:
At universities nationwide, employment of administrators jumped 60 percent from 1993 to 2009, 10 times the growth rate for tenured faculty.
One hundred students were selected at random from those enrolled at a large college.
The Difference Between Cardinal Numbers and Ordinal Numbers
A cardinal number is a number used in counting to indicate quantity. They express absolute number without any implication of position. A cardinal number answers the question “How many?” Also called a counting number or a cardinal numeral. Examples: one, two, five, ten.
But ordinal numbers, on the other hand, are position numbers. They correspond to the cardinal numbers but indicate position in relation to other numbers. Examples: first, second, fifth, tenth.
Rule 1: When a cardinal number and an ordinal number modify the same noun, the ordinal number always precedes the cardinal number:
The first two operations were the most difficult to watch.
The second three innings were quite dull.
In the first example, the ordinal number first precedes the cardinal number two. In the second example, the ordinal number second precedes the cardinal number three.
Rule 2: Use a comma between the day of the week and the month, between the day of the month and the year, and between the year and the rest of the sentence, if any.
The attacks on the morning of Tuesday, September 11, 2001, took the United States by surprise.
Do not use commas with dates in inverted order [e.g., 23 April 2016] or with dates consisting of only the month and the year [e.g., January 2017]
Rule 3: In numerals of five digits or more, use a comma between each group of three digits, starting from the right.
The city’s population rose to 158,000 in the 2000 census.
The comma is optional within numerals of four digits but is NEVER used in years with four digits.
Rule 4: When one number immediately follows another, spell out one and use figures for the other: three 100-meter events, 125 four-poster bed
Rule 5: When citing inclusive page numbers in a bibliographic entry, give the complete numbers for any number between one and ninety-nine: 4-5, 12-17, 22-24, 78-93.
You may shorten numbers over ninety-nine if they fall within the same range (e.g., 200-299, 300-399, 1400-1499) or if the second number will be clear to your reader when shortened. Numbers such as these are clear: 107-09, 245-47, 372-78, 1002-09, 1408-578, 1710-12.
Rule 6: Note that numbers used with o’clock, past, to, till, and until are generally written out as words: at seven o’clock, twenty past one.
From about.com
