Fractions are written out in words. They are hyphenated only when they come right in front of a noun, called a "direct" adjective.
...increased by seven eighths...
...only one third of them remained...
...a seven-eights increase...
...one-third reduction in staff...
If there is a mixed number, a whole number and a fraction, in the sentence also, the fraction is in figures, for the sake of consistency.
...sent 2 1/4 today and will send another 3/4 tomorrow...
Happy punctuating!
Margie