I think that they have different meanings. In English, your answer would mean "in less than a month," whereas "Under en period av en månad" refers to something taking place over the course of a whole month.
The US would say "over the period of a month" if meaning the whole month, not "during" which implies at some point within that month. I can't think of when anyone would say "during a period of a month." English teachers would put "awkward" and "vague" on it.
In another excerise it is "Under perioden från januari till mars" (or similiar) and here it is "under en period"!????? I do not understand the difference and why my translation ("Under perioden av en månad") is wrong.
In another problem, "the woman of the decade" is translated as "årtiondets kvinna", and the comments note that you couldn't say "kvinnan av årtiondet" instead. Can you explain when the genitive is necessary in phrases like this, and when the "av" construction is ok?
in a previous example i saw a comment saying that "under perioden av januari till mars" was incorrect as in swedish we don't use "av" for "of" in this kind of sentences and here there is the av
can someone explain this to me?