Good question, but I think you'd find that you can do it both ways. I think you could say årets månader or dagarna på veckan. In English it's the difference between "the months of the year" versus "the year's months" [or "the week's days" versus "the days of the week"].
One of the native Swedes would have to answer if one is more common than the other, or if the mods presented it this way to teach a lesson about word order, or for some other reason.
and one thing, I think Duolingo has mentioned in previous lectures that when we are asking questions in Swedish, it is better to use “varför då”, otherwise it sounds like a child is asking questions. So just add a "då" at the end, for instance, "varför då", "när då", "hur då", och så vidare.
Excuse me for my ignorance, but i was wondering why is på in this expression? Is The months on the year literal translation?
And why cant you say in everyday swedish Månaderna i året (The months IN the year)? I am native croatian and we would say that expression with the preposition in- The months in the year. Is that one of the things and expressions we non natives must learn by heart?
Yes, it's pretty irregular in this case. The general rule is that we don't use av the same way they use of in English, so that we will usually not want an av in this kind of construction. There are two options, either expressions with the genitive, or with prepositions, and the prepositions vary depending on the word. So it's timmarna på dygnet ('the hours of the day'), dagarna i veckan ('the days of the week'), dagarna i månaden ('the days of the month'), månaderna på året ('the months of the year').
It's not that simple.
i veckan and i månaden mean 'a/per week/month', like, I do this two or three times a week.
This one is om året and om dagen for 'year' and 'day'. en gång om dagen is 'once a day' for instance. If you think this is complicated, you can just use per for all of them in Swedish and it means the same as per in English.
i en dag/en vecka/en månad/ett år mean 'for a day/week/month/year'
på en vecka/en månad/en dag/ett år means it took someone that time to accomplish something. Jag läste boken på en vecka 'I read the book in a week' as in "it took me a week to read the book'.
'in a day/week/month/year' in English are om en dag/en vecka/en månad/ett år in Swedish and those mean 'after that time has passed'. Jag ska flytta till Grekland om en månad 'I'm going to move to Greece in a month.
And there is no rule as for "en" and "ett", right? So how do you add a word in your language? How do you know If it would be an "ett" word or an "en" word? Let's suppose that there is no similar word for a ... new plant that just has been hybridized, would it be an "en %plant%" or an "ett %plant%"?