Examine the number you are working with. Numbers 1 through 9 are written using numerals, while those above 9 are written out in words.
Decide if the number being written is a compound number. Compound numbers are those from twenty-one to ninety-nine.
Place a hyphen between the tens number and the unit number. The number 21 would be written out "twenty-one." "Twenty" is the tens number, and "one" is the unit number.
Write out fractions in words with a hyphen when the fraction is used as an adjective or when it describes something. For the fraction 2/3, 2 is the numerator and 3 is the denominator. Write out the fraction in words with a hyphen between the numerator and denominator: "The council's two-thirds majority passed the new rule." "Two-thirds" describes "majority," so it is an adjective.