There are people who will contest this point from the other side. Historical use favors the "and" http://bit.ly/2AgjOe7 but my hypothesis is that the contrary view arises from the work of American/Canadian math teachers. People will claim there's a rule about this, which makes me think it's something they were taught, but the fact the history of written use is so strong against it, it makes me think it probably wasn't the English teachers that taught it.
English is my native language. I'm a fifty year old Australian. I would only ever say this with the "and". My first thought was that the version without the "and" must be Hinglish. If it is indeed used by native speakers in some places with the "and" then those should be accepted, but should not be the default answers.
This course is Hindi from English though, not Hindi from American Mathematics!
(Native British English speaker and English educated engineer - I have never heard anyone say 'two hundred ten', much less write it. Four digit and up numbers occasionally get broken down, but as 'twenty-eight thirty', not 'two-thousand-eight-hundred thirty', for £2,830 say.)
As an FYI: In American English, we use "two hundred ten," "two hundred and ten," and "210" interchangeably in most informal contexts. I think that all three answers should be accepted. As a side note, in the US, it is not unusual to pronounce "210" as "two ten" out loud, but it is never written that way.
Correction regarding Spanish is accepted. For that matter I know perfectly well that in French 88 is four twenties and eight (quatre vingt huit), that in German, 34 is four and thirty (vie und dreizich) just as in Hindi, hence I restricted my comment to the specific bizarre "and" when expressing à hundred and something in English. In ordinary English such a comment as British English being irrational would have ben passed off as a jibe and I am sorry to have offended your innate sensitivities.
In American English, it is Two Hundred Two, In French, Deux cent deux, In Spanish, Dos ciento dos, In German, Zwei hundert drei, In Tamil, Iru nootri irandu, In Malay, Dua ratus dua, e.t.c. None of these languages/ dialects incorporates the "and". My conclusion: British English is not a rational dialect.
If you are one of the developers of this module then I suggest you have shown a very prickly reaction to some reasonable feedback. Regarding British English as an irrational dialect is low, very low, and not worthy of one trying to encourage people to learn Hindi. Would you be speaking English today if the English had not developed the language you call an irrational dialect? We are here to learn Hindi, not score point of each other. I originally asked for both the numeric form (210) and two hundred and ten to be included as acceptable answers, alongside two hundred ten. Is there a problem with that?
Well, they added the translation "two hundred and ten" almost two months ago. I'm not sure what further response on that point is necessary.
As far as the numeric form, they've said they're not doing it: https://forum.duolingo.com/comment/28889331. You'll see my opinion as to that there. Feel free to add yours. You will also observe there how course contributors/moderators are distinguished from ordinary users.