I learned about fraction(分数,ぶんすう,bunsuu) in English recently from the site below.
When you say 1/2, you can say it as a half or one-half.
When you say 1/3, you can say it as a third or one-third.
As for 2/3, you should say it as two-thirds, with s at the end of it, because this refers to a plural things and the ordinal numbers (序数,じょすう,josuu) are countable.
When you say 1/4, you can say it as a quarter, a fourth or one-fourth.
As for 3/4, you should say it as three quarters or three-quarters, with s at the end of it, as well.
Those are simpler rules than I imagined, and are reasonable, right?
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