I really got mess with the plural/singular noun! please help!

1) 80 pages
2) 80-page
3) eighty pages
4) eighty-page

I got it! Thanks, you have saved my life!

Remember that (with very few exceptions) the noun-as-adjective is always singular:

an 80-page chapter, a 10-year-old boy, a 10-minute coffee break.

vs

This chapter has 80 pages, the boy is 10 years old, our coffee break is only 10 minutes.

Mister MicawberRemember that (with very few exceptions) the noun-as-adjective is always singular:an 80-page chapter, a 10-year-old boy, a 10-minute coffee break.vsThis chapter has 80 pages, the boy is 10 years old, our coffee break is only 10 minutes.

Thanks! I am going to recite it!

Mister MicawberRemember that (with very few exceptions) the noun-as-adjective is always singular:an 80-page chapter, a 10-year-old boy, a 10-minute coffee break.vsThis chapter has 80 pages, the boy is 10 years old, our coffee break is only 10 minutes.

oops, may I ask further question?
How about the following sentences? are they correct?

This chapt

This chapter has eighty pages.

This is the only correct sentence. You could say:

This chapter has an 80-page/eighty-page appendix.

The underlined forms function adjectivally.

Oh, I found a rule form all the above example.

Is that, if a noun used as an adjective, we need to put a hyphen in between quantity (80) and noun (page) ?

Example: This chapter has an 80-page/eighty-page appendix.
if I re-write it as:
This chapter has an 80 page appendix.
which is incorrect because missing the hyphen between 80 and page.

Am I correct?

hktraderAm I correct?

Yes.

quantity-noun

The noun is singular, and there is a hyphen:

Deer can jump a ten-foot fence.
He has the record for the fastest time to eat a three-foot-long hot dog.
The marathon is a twenty-seven-mile race.