A 20-year experience

22:54 Jul 21, 2017 

I used to have a First Certificate of English text book (Oxford University Press) and I remember that there was a section that gave an explanation for number + noun (used as an adjective) + noun. According to the writers, there is always a hyphen between the number and the noun, which is in singular because it's acting as an adjective.

Two-hour film; 500-page book; 6-hour walk; Five-person family.

It gets messy when you have to refer to something like a five-and-a-half-hour talk, so I try to avoid those kind of structures!

21:35 Jul 21, 2017 

What is the process that lasted 20 years? I'd like to add my voice to Tony's and Allegro's and ask for the full context.
Tony: the hyphen is correct in UK and US English, though it's widely ignored in both.

21:19 Jul 21, 2017 

In that case, the sentence is correct as it stands, including the hyphen.

21:08 Jul 21, 2017 

Dear all:

It's a title in US English about a process that lasted 20 years (and this section compiles a company's milestones).

Thanks for all your responses!

20:57 Jul 21, 2017 

Please post the sentence containing this and tell us whether you are using US or European English

20:09 Jul 21, 2017 

I agree with Jack — the first hyphen is desirable in EN-GB, but not usual in EN-US.
However, there is no justification at all for the second hyphen; the commonest time we find it is with things like "a 5-year-old child".
However, as Jack says, I doubt this would correctly express what you are trying to say here — but we can only tell you that if you explain what it actually is you want to say?

20:04 Jul 21, 2017 

"A 20-year experience" would be possible and I see nothing wrong with the hyphen, but it means an experience lasting 20 years, which is not the same thing as 20 year experience of a particular job.