Dane here. We don't use half-third to say 2½ except for the time of day, like half-twelve is 11:30.

The way we count is indeed that way though: halvfems is short for halvfemsindstyve, literally half-five-times-twenty, meaning ½5×20 = 4.5×20 = 90.

We don't use "fems" tough. That would mean femsindstyve which is 5*20 and we say a hundred of course.

So we have this:

• 10 = ti = ten
• 20 = tyve = twenty.
• 30 = tredive = thirty.
• 40 = fyrre = forty.
• 50 = halvtreds = short for half-three-times-twenty.
• 60 = treds = short for three times twenty.
• 70 = halvfjerds = short for half four times twenty.
• 80 = firs = short for four times twenty.
• 90 = halvfems = short for half five times twenty.
• 97 syvoghalvfems = seven and half five times twenty.
• 100 = et hundrede = One hundred.