There are four in total. Just change the number before .pdf
And ETS has a sample test which is the real test in...maybe 2012. So there are five real tests available right now.
Don't be stucked in too difficult problem in REA. REA tests you on not-so-frequent concepts without explanations, which is not the direction in which GRE is getting harder. For instance, ETS won't ask you what is a Wronskian because you are likely to forget it after finishing ODE exam. Spend more time on basic analysis/abstract algebra/topology instead of strange concepts.
I am in the office and cannot type Chinese. Sorry.