(Pretending to dig out my imaginary high school/freshman hat.)
If you said between every two reals there's one rational (and between every two rational there's one real), I'd assume you meant exactly one (i.e. in the conversational sense), and then there's an equal number of them. But you said at least one, so it could be two or three, so now I'm not sure. And if there are infinitely many of them... but infinity is not even a number, so who knows?!
(Pretending to dig out my imaginary high school/freshman hat.)
If you said between every two reals there's one rational (and between every two rational there's one real), I'd assume you meant exactly one (i.e. in the conversational sense), and then there's an equal number of them. But you said at least one, so it could be two or three, so now I'm not sure. And if there are infinitely many of them... but infinity is not even a number, so who knows?!