In non-technical writing, spell out simple fractions, especially when used in isolation:
When a fraction is used adjectivally, place a hyphen between the numerator and the denominator unless either of these elements is itself hyphenated:
Fractions such as the last two, which lend themselves to confusion, are better expressed in numerals.
For the use of hyphens with fractions, see 2.11 Fractions.
It is incorrect to use th or ths after fractions expressed in numerals:
A fraction expressed in numerals should not be followed by of a or of an:
If the sentence seems to require of a, the fraction should be spelled out.
Mixed numbers (combinations of a whole number and a fraction) should be given in numerals:
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