Hi there, I have to make some assignments(7), but I don't really get them. I have to 1) tell if a set is countable 2) tell if a set has the same cardinality as R (= all the real numbers).

But I really don't get how to do this!

For example:

The intersection of Q and [3,4). How do I proof that this is countable (or not), and what about the cardinality?

Can someone help me? Explain how to do this? I have to make 7 assignments exactly like this.

Tnx,

Mary