Leif Henriksen Feb 8, 2017:

Not a KudoZ-question, but .... It depends. If you give a price, it would always be stated in digits, like kr 3,50. If a car has six cylinders, you would normally spell it out as "seks sylindre". Small numbers, ie up to twelve, are usually spelt out as words, higher numbers in digits. However, if you mix low and high numbers in the same text, it will often be more consistent to use digits only.
And there is no rule without exception – it all depends on the context at hand.