Yeah, it's as Sangoma said based on vigesimal, so halvfems is a shortening of halvfemsindstyve which means half-to-five times twenty, half-to-five being 4.5. 4.5 * 20 = 90.
Historically the Danish numbering is based on 20, rather than the English 10. So 'fems' comes from 5 x 20, so halvfems is 90
And I could write it down for the first try, with only one typo for, without ever seeing it before! Very proud of myself :D
That's what I meant to type, sorry. My question was actually about the "in one year" vs. "in a year." I typed "in one year" and it was marked incorrect.
Sorry - I didn't notice that, but mostly because I also would have thought 'one year' was acceptable, although maybe less common in this context than 'a year'.
I suspect because they want you to pay attention to the difference between "one year", and "a year". What was said was "A year"' = et år, and not ´"one year" = én år.
'One year' would still be 'et år', unless you want to stress that it's just one year, then it becomes 'ét år'. (Still of neutral gender)
I think 'one year' should be accepted as an answer (and probably is by now - I didn't check) since it really doesn't make a difference.