Typically speaking, there is no significant difference between "two thirds" and " two-thirds". Which one to use is mostly a matter of style and is not.
Use a hyphen between the tens and units number when writing out the numbers twenty-one to Incorrect: Two-thirds of the Senate overrode the veto. (Here two.
I have seen 2/3 written as two-thirds or as two thirds. Are both ways (with a hyphen, without a hyphen) acceptable, or is only one truly correct?.
Generally, hyphenate two or more words when they come before a noun they Rule 3. An often overlooked rule for hyphens: The adverb very and adverbs.
For instance, do you need hyphens in long numbers when you write them as words? Or in ages? What about in a fraction, like 'two-thirds'? Find out here.
Compound adjectives are not usually hyphenated in the predicative (when they two-thirds three-quarters seven-eighths. The dash, however, not the hyphen.