"Do you have strings?"
Translation:Har ni snören?
There is. According to my notes, this is the so-called "fourth declension" in Swedish: ett-words ending in a vowel. The indefinite plural form adds an "-n" (snören), while the definite plural form adds "-na" (snörena). They occur much less frequently in the lessons than ett-words ending in consonants (the "fifth declension"), which are unchanged in indefinite plural, but add "-en" in definite plural form. As a result, I still forget about this distinction :-)
I'm quite surprised too, that they're talking bout strings all the time. But maybe Duolingo want to stress that Swedish are just a mighty nation of melodic death metal and they just break their strings quite often so they ask this kind of questions instead of "have you seen my wallet/keyes/cell/glasses"?
As suggested i checked all the above discussion and there is no clear explanation of why we should choose the definite form over the indefinite one. There are some useful hints, though.
Snöre ---> indefinite singular Snören--> INDEFINITE plural Snöret --> definite singular Snörena-> definite plural
As suggested below by Natalie it's like the old good "äpple". This is how it works for every -ett word ending with a vowel (exceptions apply)
So "Har ni snören?" is actually built up with the indefinite form, and this should answer your question.
Maybe it is dumb question, but how many people in Sweden use «du» like «ni» and like «du»? And isn't it roughly if I say «du» when I talk with a stranger? (p.s. sorry for my English, I'm just from Russia)
That's actually a common myth. Some people in customer service do use ni as a formal "you", but this is rare and it's a largely incorrect usage. Swedes simply don't use titles and formal pronouns. You could even say du to the king.
(And it's not a dumb question at all!)