Стакан in Russian is a cylindrical or slightly conical vessel without a handle. The hight is expected to be bigger than its diameter. The material may not be glass, and may not even be transparent, although traditionally it is glass.
Стакан is a popular measure of volume for liquid and dry substances, e.g. in cooking, and comes surprisingly close to the US cup: 250 ml vs. 237 ml. In this phrase it is obviously used in this capacity.
Because Стакан is also a Russian measure here (of rice). It's the equivalent of a "cup" in English.
I quote HartzHandia: "Стакан in Russian is a cylindrical or slightly conical vessel without a handle. The hight is expected to be bigger than its diameter.
Стакан is a popular measure of volume for liquid and dry substances, e.g. in cooking, and comes surprisingly close to the US cup: 250 ml vs. 237 ml. In this phrase it is obviously used in this capacity."
If they do not satisfy you, report the answer you consider correct. It is a beta, it is normal that they don't accept all translations right away. But if you talk about a "cup" of rice in English, you would say a "stakan of rice" in Russian, so using another word in both sentences may just not be that correct.
But I understand your frustration, you wish you would read a sentence and that you would be able to just write the right stuff, but Duo forces you also to discover the "good" way to translate all and sometimes litteral translations are not that good.
Kind of complicated. "Стакан" means "glass". "Cup" is "чашка", and a cup of tea would be "чашка чая". So why is "cup of rice" accepted for "стакан риса"? The English measurement called a "cup" (236 ml) is called a "стакан" in Russian. It makes sense to measure rice in cups, but not generally tea.
You're incorrect. If you measure everything in cups, it's size doesn't matter. Bc two cups is still double of one cup. Only overall quantity will be different. But for cooking, it serves good use as as a kitchen measure. Also there's mostly no need to be over-pedantic with measures in cooking, as everybody have their own taste anyway.
I'm confused. Cornell says that the partitive is an old-fashioned way of saying 'some' uncountable objects (http://russian.cornell.edu/grammar/html/le71_78_a.htm). In addition, this Duo exercise is in the lesson on the partitive case.
Rice being an uncountable object (under normal circumstances), why are we using the genitive here? Is it because we're not saying 'a glass of some rice', so much as 'a measure of one glass of rice'?
Have you read any of the comments explaining the use of стакан? In all languages there are words that have different meanings in different contexts. Стакан does not map one-to-one with "drinking glass" in every case. And please, delete from this comment any abbreviated profanity.