The intervals $(2,4)$ and $(-1,17)$ have the same cardinality I have to prove that $(2,4)$ and $(-1,17)$ have the same cardinality. 
I have the definition of cardinality but my prof words things in the most confusing way possible. Help!

The general way to show two sets $X,Y$ have the same cardinality is to show that there is a function $f:X\rightarrow Y$ that is both 1) injective and 2) surjective. That is  1) for all $a\neq b\in X$ we must have $f(a)\neq f(b)$ and 2) for all $y\in Y$ there must exist $x\in X$ such that $f(x)=y$.
