one third or one-third
Hello,

My question is about the hyphen.

1. The moon is bout one third as large in diameter as the earth.
2. The moon is bout one-third as large in diameter as the earth.

Sentence one is correct. I suppose that sentence 2 might not be incorrect because one-third is used as an adjective like in a one-third cake.

But both "the three-hour movie" and "the three hours' movie" are correct, and both "three-fourths of the surface" and "three fourths of the surface" are correct. So I'm confused about how to use a hyphen correctly.

Thank you.

Question

one third or one-third
Hello,

My question is about the hyphen.

1. The moon is bout one third as large  in diameter as the earth.
2. The moon is bout one-third as large  in diameter as the earth.

Sentence one is correct. I suppose that sentence 2 might not be incorrect because one-third is used as an adjective like in a one-third cake.

But both "the three-hour movie" and "the three hours' movie" are correct, and both "three-fourths of the surface" and "three fourths of the surface" are correct. So I'm confused about how to use a hyphen correctly.

Thank you.

Answer

When you are writing out fractions with words, you should always use the hyphen.  So, "2. The moon is about one-third as large in diameter as the earth. " is the correct sentence. Also,  "three-fourths of the surface" with the hyphen is correct, the one without the hyphen is not correct because "three-fourths" is a fraction and should always have a hyphen when written out with words.
 https://www.proofreadnow.com/blog/bid/88251/Hyphens-Fractions-Numbers

This is a different rule from the one about compound adjectives like "the three-hour movie" . 
In "three hours' movie" I believe this apostrophe is a temporal expression which you can read more about here:
https://www.grammar-monster.com/lessons/apostrophes_in_time_(temporal)_expressions.htm

Answers · 1

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