"Learned Numbers" my arse
Apparently I've "learned numbers" except that the only numbers I came across were Ein, zwei, drei, vier, sechs, neun, and zwölf, along with erste and dritte.
So really I've only learned seven numbers along with another form of two of those numbers.
That's weird. Now, I haven't gotten to the numbers, or maybe I just don't remember, but Duolingo is not going to teach everything I guess. Part of learning a language is having curiosity about it. You can't expect to learn everything in here.
I recommend getting really involved with the language you want to learn, I think that's probably why learning English is so easy nowadays, it's everywhere.
Anyway, I think Duolingo should teach the first 10 numbers and explain how to form every other number one might need, but you should still be able to find whatever you want to learn, and Duolingo doesn't offer, somewhere else. You can't learn a language in a single place.
Couldn*t agree more with the comment above but to make it easy for you: Eins, zwei, drei, vier, fünf, sechs, sieben, acht, neun, zehn, elf, zwölf, dreizehn (= 3+10, 4+10, 5+10 ... 9+10 = neunzehn), zwanzig (20), einundzwanzig (notice the missing "S"), zweiundzwanzig (2+und+zwanzig), 3+und+20=dreiundzwanzig, neunundzwanzig ..., dreißig (30), eiNunddreißig, .... neununddreißig, vierzig (40), fünfzig(50), sechzig, siebzig, achtzig, neunzig, neunundneunzig, einhundert (100). einhundertundeins (101) ... pretty simple if you think about it. good luck with the language!