"How many oceans are there?"
Translation:Có bao nhiêu đại dương?
I can never figure out where to put bao nhiêu. Sometimes it's at the end, sometimes at the beginning, sometimes in the middle. Gah.
... and why is 'mấy' not ok? There are - as far as I know - less than ten oceans on earth...
If you ask, how many oceans are there on Jupiter, then "ở đó" refers to Jupiter. Since there is no context, we would assume the question is about earth's oceans, and therefore, it would be odd to add "ở đó".
I think this is where the English "are there" is different from the Vietnamese "ở đó." In English, "are there" also means "exist" while "ở đó" just means "over there." So "bao nhiêu đại dương ở đó?" = "How many oceans are over there?"