Fractions and compound word confused me:

Five sixths

One third

And two hours

Two hour

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  • 1
    Could you rephrase the question? It's not clear. – Varun Nair Sep 20 '17 at 5:46
  • Expressions like "two hour" might sometimes lack the expected s at the end because they are adjectival phrases used predicatively. For example we have a two hour delay or a three mile walk, not a two hours delay or a three miles walk; but we would say that the delay was two hours and the walk was three miles, with plural s, because of the word order. It would seem possible for fractions to behave that way, but to me examples sound better with that s: a two-thirds completed questionnaire, a three-quarters empty lecture hall, etc. – Chaim Sep 20 '17 at 16:31
  • Or were you asking about the dash sometimes separating the words in expressions like those? – Chaim Sep 20 '17 at 16:34

Let me help you out by writing down some denominators.

Half, Third, Fourth (or quarter), Fifth, Sixth, Seventh, Eighth, Ninth, Tenth...

And so on, with every subsequent number having 'th' attached to the end to make it represent a denominator in a fraction.

Now, the reason why there can be an s after the 'th' is because fractions can be singular or plural

For example, you can have one fifth of cake, or you can have two fifths of a cake.

In other words, if any fraction has the first number be greater than one it will be written plurally with an s

1/8 is one eighth. 3/8 is three eighths. 1/15 is one fifteenth. 6/15 is six fifteenths

Now, let's address the second part of your question.

You would not say "two hour", you would say two hours. The adjective "two" shows that you do not have a single hour, but that have more than one. Thus, the word "hour" must be plural, not singular. We pluralize words by adding an s. Thus, it is two hours.

  • Personally, I always hyphenate fractions. Two-hour is possible when it's an adjective It was a two-hour meeting. Quantities, lengths of time are always singular as adjectives. A two-pound bag of sugar, a ten-dollar bill. – Matt Jan 2 at 21:25

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