Some authorities say that the numbers
one through
nine or
ten should be spelled out and figures used for higher numbers. Other authorities spell out
one through
one hundred, plus even hundreds, thousands, and so on. The best strategy is to be consistent.
Correct Examples: I want five copies, not ten copies.
I want 5 copies, not 10 copies.
For further rules see here
Rules for Writing Numbers
and here
Writing Numbers