Possible Duplicate:
Pluralization rule for “five-year-old children”, “20 pound note”, “10 mile run”
According to Google, it is correct to say "two-week business trip" instead of "two-weeks business trip". So "week" word should be used in singular form which looks strange for me as non-native speaker. Is there any special rule for this kind of phrases?
I believe these are known as noun adjuncts (Wikipedia). It's a grey area and unfortunately there are no hard and fast rules. I would say that it's a two-week business trip because one would have originally said two-week long business trip (Edit: which on reflection, is just the same... Never mind)
However something may take place "in two weeks' time" or "in one year's time". See the extract from Fowler on the Wikipedia page.
