Bonjour Louise, I think your response is correct and this does seem to be a programming miscue. I am not aware of any grammar rule that requires to use the number (10) in lieu of spelling it out. Bonne chance. Ron

I was marked wrong when I spelled out dix minutes but it was because I misspelled Marseille. That was explained to me when I reported the issue.

And I wrote dix minuts, forgetting the final e of minutes, It seems to me that mispellings like that and Marseille spelled wrong should be yellow errors, not red.