I am wondering whether the following forms are all okay:

  1. It was a 3-hour round trip to work.
  2. It was 3 hours' round trip to work.
  3. It was 3 hours round trip to work.

I'm sure #1 is correct. What about 2 and 3?

I'd appreciate your help.

  • Yes, the article ("a 3-hour round trip") is expected, but not always used. – Andrew Jul 17 '17 at 16:39
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    Related: ell.stackexchange.com/questions/14290 – user3395 Jul 17 '17 at 17:10
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    Actually, none of them but 1 is the closest. A round trip is a trip to a destination and back to the starting point, so you should say something like "It was a 3 hour round trip to work and back". – Rob K Jul 17 '17 at 17:11
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    @RobK Good point (+1) ! The counterargument would be that "and back" is already implied by "round trip", so specifying a point of interest ("to work") makes sense. Flight bookings use this convention. – Lawrence Jul 17 '17 at 17:22
  • When the Saxon genitive is applied to a quantity (of time, distance, weight, etc.) it serves as a determiner, so the article is omitted. Thus, No. 2 is fine, but not No. 3. No. 1 is also acceptable and idiomatic. – P. E. Dant Reinstate Monica Jul 17 '17 at 18:46

You asked two things:

  1. What part of speech is round trip? 2 Which sentence is correct?

    1. In the first sentence you are using round trip as a noun (round trip is defined as a return journey).

It is being modified by what we call a compound adjective* ( **three-hour which describes how long the roundtrip journey will take).

The first sentence is correct because when you use a compound adjective the number part is always singular i.e. three not 3s. (see below about how to write numbers).

Other examples of compound adjectives are: -two- metre rope. -three- month break. -six- page document. -ten-minute walk. -ten- minute wait.

Notice the first word of each adjective is singular and that the adjective form is hyphenated although some texts don't hyphenate.

In you last two sentences you used plural forms of three which is wrong for this type of adjective. Also, you must write numbers from 0 to 100 as words according to the Chicago Manual of style.

I hope that helps in some way.

sources: Collins dictionary and Grammar for English language teachers by Martin Parrot

  • Self correction to the above. In compound adjectives the second word is always singular. Of course the first word is plural e.g three day week and NOT three days week. Sorry for my error. – user242899 Jul 17 '17 at 21:52
  • Please use the edit feature to make corrections instead of using comments. – snailplane Jul 20 '17 at 17:36
  • In the last two sentences, "3 hours" is functioning as a noun, and "round trip is modifying it. A similar structure is "It was hard work clearing the driveway"" "hard work" is a noun phrase, "clearing the driveway" modifies it. Also, "3" versus "three" is a matter of style, not grammar (Notice it's the Chicago Manual of Style). Saying one must follow the CMS is rather strong. – Acccumulation Mar 21 '18 at 15:48
  • trip is a noun in all three: round trip versus one-way trip – Lambie Aug 27 '19 at 14:12

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