Translation:Are taxis fast?
A don't no. My "is taxi fast?" as wrong too. Why did the translation suddenly become plural?
Because you didn't say "the taxi" -- if you forget articles on singular nouns, Duolingo tends to correct it to plural instead.
You technically do not know. Japanese can be very ambiguous relative to other languages because plurality, and even subjects, are often not stated explicitly but must be inferred from context. For example, the simple sentence "oyogimasu" can mean "i swim," "he swims," "she swims," "they swim," "i will swim," "he will swim," "she will swim," or "they will swim." 8 possible meanings for one word, since the subject is not specified and that form can indicate present or future tense. Context would be necessary to determine the exact meaning.
Exactly why the Duo should provide answers in the singular and plural. It makes no sense to give as wrong when no indication of number bending in Japanese text. "is taxi" or "are taxi" both are correct.
They do accept both singular and plural, as long as the sentence is grammatically correct. To be clear: neither "is taxi" nor "are taxi" is correct, it should be either "is the taxi" or "are taxis".
To add, since there is no context specifying what taxi is being reffered to here, it is best to assume that all taxis are.
In this context taxi requires an article in English. Either the definite article "the taxi" or the indefinite article "a taxi"
Unfortunately duo marks "a taxi " incorrect as of 1 Nov 2017 . I reported that though because Japanese doesn't use "a" or "the " and we have no context.
I said "is a taxi fast", but it was incorrect. How would you say that instead?
Is "A" taxi fast/Is "THE" taxi fast - in Japanese there is no distinction in this situation. Either of these, as well as the suggested solution should be acceptable in this instance. Please advise.