I agree. Formally, English may require the second "an" but in everyday conversation this shortcut is often deployed by native speakers. These aren't English lessons, so ambushing native English speakers with their little quirks that aren't exactly standard is a distraction, not a help.
what you have written means "do you want apple, or orange" (this is a yes/no question which is asking the person whether he wants any 1 (or both also) of the fruits) what the question asked by duolingo is "tujhe seb chahiye ya santra" which means "you want apple, or orange" (the question is asking the person to choose what he wants, apple or orange)
I got this wrong initially for selecting "Do you need an apple or orange"...this seems like an error with my English rather than my Hindi and since the word "an" is not specifically part of the Hindi, since there are no articles, not strictly fair
Well, in your example ("Do you want an apple AND an orange?"), the expected answer is "yes" or "no", not "an apple" or "an orange". If I understand correctly, this changes things in Hindi. I believe you would have to say "क्या तुझे सेब और संतरा चाहिए?". Maybe a more experienced Hindi learner can confirm?
I believe this is a trickier example. If what you mean to ask is whether the person wants to eat at all (whether am apple or an orange is secondary to the facet that they want to eat), then “kya” makes sense. If what you mean to ask is specifically which fruit they want to eat, then you should not use “kya”. There is such a case in one of the exercises.