"Your answer is wrong."
Translation:Η απάντησή σου είναι λάθος.
Yes, it's a neuter noun for error/mistake. But then the En translation doesn't sound quite right either if you're using λάθος as a noun.
IIRC it's used elsewhere in the Duo course as an adjective for incorrect or wrong, but the word I've encountered more frequently outside of Duo is λανθασμένος. In fact, now that I think about it, I've never actually seen λάθος as an adjective outside of Duo... and it's not in my Oxford or El Wiktionary as an adjective either. Dimitra, Troll, D_.., Mizinamo - or any other helpful Duolingoers - are you able to help us out?
It sounds fine to me -- using the noun as a quasi adjective, even attributively (η λάθος απάντηση, etc.).
My feeling is that there's a slight difference between η λανθασμένη απάντηση and η λάθος απάντηση -- from by belly feeling, I would say that the first one is an answer that you arrived at for the wrong reason or through the wrong way, while the second one is simply incorrect. Or that the first is an answer that contains an error, while the second one is simply the incorrect choice out of several possibilities: it is not incorrect as a sentence but inappropriate. Not sure how to put it in words. Perhaps I'm also just imagining it :)
But long story short: Η απάντηση είναι λάθος / η λάθος απάντηση sound fine to me, even though λάθος is technically a noun.
(And I'd always use it in the singular: H απαντήσεις είναι λάθος / η λάθος απαντήσεις, for example.)
Incidentally, the first collocation that came to my mind, λάθος πορτα, has zillions of hits on Google, including several songs about "knocking on the wrong door".
So it's not just a Duolingo usage :)
mizinamo, is it common in Greek to use a noun like "λάθος" as an adjective, i.e. "wrong" in this case? I would prefer the adjective "λανθασμένη" but that is my personal preference even though there is a very small difference between saying "your answer is a mistake" compared to: "your answer is incorrect or wrong". For example an answer could be a mistake if it is going to have dire consequences but an answer is incorrect or wrong if it is not factual.
This was given to me as a "Mark all correct meanings" question with the answers: 1) Η απάντησή σου είναι λύση. 2) Η απάντησή σου είναι λάθος. 3) Η απάντηση σου είναι λάθος.
I chose 2, but it told me that 3 is also correct. Technically it's incorrect as there need to be 2 accents in such a case.