Translation:My friend wants to buy a bag of apples.
only about 2 sentences before in the same lesson it wouldn't accept it when I translated 要 as wants, so in this example I got with the programme and translated it as "my friend needs to buy a bag of apples" and it now decides it will only accept wants
Yes! Either it should accept both "want" and "need" or it should accept only one of them. Previous question didn't accept when i wrote "want" and now this question doesn't like "need". frustrated
So can "一袋" and "一包" actually be used interchangeably or is there any difference?
They are very similar and we don't differ these two classifiers too much, but 一袋 sounds like the bag is opened, like a plastic bag, and 一包 is used more for a sealed bag, like chips. Sorry that my English is not good enough to explain this well, and I believe this difference depend on regions, or even depend on speakers, so you can just take this as a reference :)
要 can also be used to express future intention - so they should also accept "My friend is going to buy a bag of apples" - right?
That would be "My friend will buy a bag of apples.", which I think is a technically correct interpretation. I've no idea if it's accepted though.
("Going" is progressive tense, which hasn't been taught yet, but Duolingo has allowed that in several other exercises while rejecting it in others, so I'm not sure what should be accepted.)
'has to buy' would be more appropriate than 'wants to buy'. Otherwise, make it into 想要, to make it less misleading/
Another ridiculously narrow choice in answers
It won't take "My friend wants to buy one bag of apples". I've always written "a bag of apples" but I thought I'd try the other alternative. This one is absurd because it accepts "one bag of" in many other examples throughout the questions. Yi, or 一 means one.