I'm sad because I always write "least" instead of fewest"... it means the same in this context doesn't it? xD
Even most native English speakers say "least" these days but it is still contentious so "fewest" more correct with countable nouns like "people" and "least" should be used only with uncountable nouns like "milk".
On all the Duolingo courses I do, many people in the forums are very insistent on the most correct English. That seems to be less in the Vietnamese course.
My view is that "least" should be accepted because even native speakers say it, but "fewest" should be the default answer because it's still regarded as wrong in the English-speaking world just like "ain't" and "gonna" etc.
Why isn't nhất immediately after ít in this case? bạn tốt nhất = best friend but ít người nhất = fewest people
Follow-up: Would the most people then be "nhiều người nhất"?