Well, "welchem" is the der/das (male/neutral) form of "welch." "welcher" is the female form, because "mit" takes the dative case; thereore, any object that complements "mit" must be in the dative case, so basically, only "welcher" and "welchem" may be used after "mit," it just depends on the context. If you're talking about dogs, you'd use welchem, if you're talking about cups, you'd use welcher.
In case no native speakers decide to drop by, take a look at this link:
There you'll find that it says "mit" is a dative-only preposition (some prepositions can take either accusative or dative), and just a lot of information on dative with prepositions in general.
In the dative case, ”der” ”die” ”das” ”die” becomes ”dem” ”der” ”dem” ”den” respectively. ”Welche” takes the same endings: ”welchem” ”welcher” ”welchem” ”welchen”. The plural also requires an ending ”(e)n” for the noun that folows the determinant.(so it will be ”welchen Kindern”.)
It seems like the confusion here is why Duolingo chose the feminine form. Normally I'm guessing this would normally be determined by the context of the previous conversation, for example, if you were talking about something relating to chairs (Der Stuhl), you would say 'Mit Welchem?' to ask which one specifically (because Stuhl is masculine). Since there is no indication what the previous context is, we can only assume that they are talking about a feminine object, but for the purposes of the translation, this doesn't effect the genderless English translation of this sentence.
I put "Which with?" and it was marked as wrong. I actually did that because words are usually inverted (in comparison to non-question sentences) for questions like "Isn't it?" "Aren't they? Can't he?, but I see that this is not the case for questions like "For when?", "With whom?" (formal, technically correct, least used) and "With who?" (informal, technically incorrect, most common), or "With which", since they can all be written the same way in non-question phrases. "What about...?/How about...?" seems to contradict this, but since it has to include at least a third word on the question ,then I suppose it doesn't count. What a mess!! Mess a what?? Any clues ???
Yes, but in both cases (with and without the apostrophe) you have to invert the beginning of a sentence in comparison to the non-question one. I just want to know if there's a rule or norm explaining in which cases you should invert the beginning of a question, and in which cases you shouldn't.
'Mit welchem' and 'Mit welcher' would've been both right.
welche and welches are not right, since mit is a dative verb and dative transformations are such:
der -> dem das -> dem die -> der die (plural) -> den (Die Kinder -> den Kindern)
there's no 'es' or 'e' ending.
In this case, the 'unknown' is a feminine, like Tasse. If you were instead talking about a masculine thing (Tisch) or neutral (Buch) , you'd use welchem.
Ich denke nichts.
'whom with ' (mit wem) is used in context of people. 'With whom' are you going to the zoo?
In this case, 'with which one' is for things, e.g.:
'I'm going to cut this board with the help of a knife"
(There are a lot of knives lying there, so the other guy asks)
with which one?