Please help me with these questions! Any ideas or hints or anything would be great. We've had exactly one lecture on this, and the book has no proofs, so I'm struggling with how to formulate proofs for this type of thing. Here are the problems and my ideas so far:

1. Show that for real numbers $\displaystyle a$ and $\displaystyle b$ with $\displaystyle a<b, (a,b)$ has the same cardinality of $\displaystyle \Re$.

I know this interval is uncountably infinite like $\displaystyle \Re$, and I can use Cantor's diagonalization argument to show that. Is this all I need to do?

2. Suppose $\displaystyle A$ and $\displaystyle B$ are sets such thatcard$\displaystyle A$ $\displaystyle \leq$card$\displaystyle B$. Prove there exists a set $\displaystyle C \subseteq B$ such thatcard$\displaystyle C$=card$\displaystyle A$.

I'm trying to use the regular existence proof idea, in the sense that I'm trying to think of a "Consider this set C and the bijection f:A to C" and so on, but I can't think of anything that applies to an abstract set. A could have its elements as numbers, functions, subsets, etc. and all the things I can think of require something to be known about the set.

3. Suppose that $\displaystyle A, B$, and $\displaystyle C$ are sets such thatcard$\displaystyle A$ <card$\displaystyle B$ andcard$\displaystyle A =$card$\displaystyle C$. Prove thatcard$\displaystyle C$ <card$\displaystyle B$.

I'm totally lost on this one... It seems obvious, so I think I'm having trouble separating the properties of finite sets with the properties of infinite sets.

Thank you!!