I gave 'You all are Tanzanians" and it corrected to 'You are Tanzanians' Can someone explain why the Singular Ninyi is used here with the plural Watanzania to not produce you all?
If pointed at a singular person i.e. Ninyi or Mimi I'm unsure as to when to use 'Watanzania' vs. 'Mtanzania'
Your original answer was correct. I was actually going to put the same answer, but changed my mind. In English, "you"can be used both in relation to one single person, or multiple persons. I think "you all" is marked wrong because "ninyi" doesn't literally translate to "You all". Since Swahili uses two separate words to differentiate between the singular (wewe), and plural (ninyi) "you", it wouldn't be necessary to use "you all"when translating because it is already implied, and should be mutually understood.
Ninyi is plural therefore Watanzania would be used. Wewe, and Mimi are singular therefore Mtanzania would be used. Example: Ninyi ni (Wa)tanzania. You (Pl.) are Tanzanian(s). Wewe ni (M)tanzania. You (Sing.) are Tanzanian. *"Wa-" and "M-" both serve as prefixes that change depending on the subject. This system of prefixes will be very important in furthering your understanding of Swahili. Check out some of Sayi Micheal's tutorials on YouTube. His channel is called, "Swahili Dar Language School". I hope this helps.