Why is "The man has a black pair of jeans" wrong?
It's not wrong. That's what i wrote, and it was correct.
No! The French sentence is surely saying that the man has one pair of jeans. But the " The man has black jeans" is not precise and could mean that the man has a number of pairs of black jeans.
For French "in jean" Duo sometimes uses "a pair of jeans" and at some other times it uses only "jeans". This is confusing! What's the underlying principle?