Pronounce German back letter "R"
Am using Duolingo to brush up on Spanish and German. When I have to pronounce the back R...I get counted wrong every time! I have to flip or roll the R like Spanish or Italian. I was born in Germany. My Mother is German. Therefore I am quite confident about when to pronounce letter "r" towards the front or back. Good thing I studied Italian diction in music school. Still Duolingo is frustrating me with pronunciation practice in German.
The pronunciation practice is unreliable at best. One time my brother said "Deine Mutter" instead of whatever it was that he was supposed to say and it was accepted. If your mother is German I would ignore the pronunciation practice on Duolingo and just talk to her, it will be far more useful.
Even among native speakers, not everyone uses the same sound for "r" -- some have a fricative, some a trill, some even an approximant very similar to the one most English speakers have.
If Duo's pronunciation practice is not helping, I'd recommend turning off the microphone in your Duolingo settings.