General english grammar rules for using numbers in your writeups:

  1. If a number must be used at the beginning of a sentence, spell out the number.
    Example:
    4 score and 7 years ago...
    Should be:
    Four score and seven years ago...

  2. Spell out numbers that are one or two words in length.
    Examples:
    There are 9 innings in a baseball game.
    She placed her two hundred sixteen dollar bet on the 3-legged horse.
    Should be:
    There are nine innings in a baseball game.
    She placed her $216 bet on the three-legged horse.

  3. Use numerals when writing dates, times, addresses, decimals and fractions, percentages, exact amounts of money and statistics.
    Example:
    After she won two thousand thirty three dollars and twenty nine cents, she bet the entire amount on the Mets beating the Yankees five games to one on october twenty-ninth, two thousand at nine-thirty at night. Should be:
    After she won $2033.29, she bet the entire amount on the Mets beating the Yankees 5-1 on October 29, 2000 at 9p.m.
    In all reality, this sentence should be broken up into several different sentences, but I included it to show how numbers can be confusing when they are not done using standard rules of grammar.