"The plate and the cup are on the table."
Translation:Patella et poculum sunt in mensa.
Sometimes I honestly make a one-letter typo and my answer is rejected. Other times I really don't know something and my answer is accepted. Like in this case, I wrote, "Patella et poculum in mensam sunt." (I actually used the hover feature to see if "mensa" was inflected, and it showed "mensam.") I see in the suggested answer there is no "m" on "mensa." So is my answer wrong?
Because location in + ablative ("ablative of place"). Not in+ accusative.
In + accusative is only "into".
Do not use the dictionary to see if the word is inflected, it's misleading, and a very bad way to learn. Instead, rely only on your logic, even if you make some mistakes.
Considering what is the preposition (and what is the case following this preposition usually) and what is the kind of action (throwing something, going somewhere or from: the movement of the verb).
I totally agree with the explanation above. Regarding typos: I might be wrong but I think that Duolingo accepts a one-letter typo as long as it does not change the meaning or a grammar form of the word and still looks like, well, just a typo. When you write 'thw' instead of 'the', Duolingo is okay with that but try to mix 'you' and 'your' - no mercy :) That's what I observed.