How credible is Duolingo? I've heard many bad things about its grammar in Asian languages so I just wanted to see if they got this specific thing right. One of the Questions it asked was how to translate: "How many tables are in the room?" I initially got it wrong for a different reason but when I got it wrong the second time I realized it wanted me to put both "に" and "は" right next to each other. Is this correct on Duolingo's end, or am I overthinking it? Are there just multiple ways of answering it that are both valid? I've attached the screenshot of the question if I have worded this weirdly.
Duolingo is not really good for grammar. The course has been a bit abandoned. If you pay attention, compared to other courses, the variety of exercises is very few, etc.
Both sentences with は or without は mean the same. The thing is that by using は, it seems that it is already a known information.
So, if someone asks about an unkown room:
You might say (because you know about the room already):
It could be also a comparison:
刑務所に部屋がいくつありますか How many rooms exist in the prison?
You could say:
刑務所(は)知らないが、私の家に(は)三つの部屋があります I don't about the prison, but there are three rooms in my house.
There are MANY other uses for the は particle that will come to see at some point. Many linguists have written many articles about it, so it's kind of impossible to talk about every use.
Duolingo is simply not considering these kind of nuances.
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