Translation:He is a quarter Norwegian and a quarter Danish and a half Greek.
Interested in views on this of other native English speakers... "He is a quarter Norwegian and a quarter Dane and a half Greek" also "feels" right to me. He's half Pole, Half Romanian would also "feel" right, while accepting that half Polish, half Romanian would be correct too of course.
I'm sure I've seen other Romanian sentences on Duolingo where a "comma" is used in place of the first "and" meaning, this should be:
"He is a quarter Norwegian, a quarter Danish and a half Greek"
This translation is what we'd say in English, and is what I thought would be said in Romanian.
Further, the Romanian should be:
"El este un sfert norvegian, un sfert danez și o jumătate grec."
Am I understanding this correctly? Has Duolingo made yet another mistake?