@Joe Nation,
Be happy you did not have to learn the oldfashioned counting in Danish. Say up til WWII and later by older people.
Tres -60 - was earlier tredsenstyve = (3 x 20)
Firs - 80 - used to be firsendstyve = 4 x 20)
Halvtres -50 -Halvtresendstyve means 2½ x 20) translated halfthreeandtwenty
Halvfjerds - 70 -Halvfjerdsendstyve 3½ x 20)
That´s enough.
I as a Swede learnt that as a preschool kid. Gosh - did I make many mistakes in counting in Danish the rest of my life.