Chociaż uwielbiam język polski całym sercem, jest bardzo, bardzo trudny. (Patrz na te numery, na przykład) :P Ale nigdy nie poddam się! Wszystko jest możliwe. Nauczę się polskiego, nawet jeśli to jest ostatnie działanie moje!
Is there a logical reason why 40 ends with dzieści, while all the higher multiples of ten have dziesiąt?
dziesięć, dwadzieścia, trzydzieści, czterdzieści, ... then the logic starts. The logic being five tens (pięć x dziesięć = pięćdziesiąt). I am no expert in languages let alone in polish, but as often is the case sound often decides. The first few would just sound odd and strange with "dziesiąt" as an ending.
I don't know. It could have something to do with the dual-plural merger doing different things to numbers 2-4 and to 5+, but don't cite me on that.
Is not that numbers 2,3,4 take a nom. plural, and 5 and upwards take a gen. plural?
Possibly in relation to Russian or Ukrainian. Тридацят, сорок, пятдацят. 30, 40, 50. Forty is a unique #.
Perhaps I'm hearing incorrectly, but is the audio not pronouncing the ć in pięćdziesiąt and the ść in sześćdziesiąt? Do those consonants usually get slurred over in quick/everyday speech?
No, they do not usually get slurred. But in these two words, it is indeed a bit too much to pronounce them clearly. So while 99% of Polish is read exactly as you see it and there are no vanishing sounds, these are kind of exceptions.
So I understand that forty is the technically correct spelling, but fourty is such a common mispell. Shouldn't it be marked as correct with the note of a mispelling, rather than completely incorrect?
Perhaps. The problem is that the course creators has no control over what is marked as a minor misspelling and accepted and what is marked as outright incorrect. You might try contacting Duolingo staff directly.