The difference between "weeks" and "week"

[Aryam]

hi

We are leaving for two weeks.
We are going on a two-week vacation.

I would like to understand why we add "s" in the first sentence and we deleted in the second sentence, i want want the explanation of both sentences..
Best Regards

[Mister Micawber]

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In the first, 'two weeks' is a noun phrase. In the second, 'two-week' is an adjective. English adjectives do not inflect for number.
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Native English teacher at Mister Micawber's

[Aryam]

Thank you Mister Micawber

Best Regards