"You are fairly fit."
Translation:Du bist ziemlich fit.
When I was in Germany and vaulted over a gate on a walk in the countryside, my girlfriend said something like "Du bist Sport fit!" and giggled. The thing is it sounded like "Du bist Spott fit!" which I interpreted as "You are fit for derision!" - we weren't getting along very well at the time so I didn't ask her to explain.
It can also be an adverb or even an adjective, as in this couplet, by Janosch:
Die Ente schießt mit etwas Schrot Den Entenjäger etwas tot.
Translation: The duck shoots with some bit of lead The duckhunter somewhat dead.
Hey, it even rhymes in English! At any rate, this Duolingo sentence is correct in German.