"We have seven kinds."
Translation:Vi har sju sorter.
'tyve' is accepted in Riksmål, a more conservative form of Bokmål.
It seems 'tyve' and 'tredve' was accepted in Bokmål 2003-2005, and 'syv' still remains. You could probably used them without trouble in Norway, but as there is a strive to use the correct forms as often as possible in this course, they shouldn't be accepted.