Fractions that stand alone are written out in words. They are hyphenated ONLY when
they are right in front of a noun as a direct adjective.
...up by three fourths...
...two thirds of the group...
...increased by seven eighths...
...a three-fourths increase in debt...
...two-thirds vote of the council...
...seven-eighths cup of liquid...
Fractions that are a part of a mixed number are in figures and are not hyphenated because they are already considered to be a unit.
...sent 1 2/3 to them...
...up by 7 3/4...
...a 4 3/5 increase...
Happy punctuating!
Margie