hi,
well, to be honest i dont see any reason as to why anyone who has access to this website should fail any of the exams you just stated. That means you not spending enough time on research, which should be part of you, if you trully want to be an oracle dba........take your time and get enough resources/books and READ. Once you done doing that and understand how things flow inside the database, seat down and query dbasupport and i gurantee you'll pass all the exams. there plenty of articles/white papers at otn.oracle.com talking about resource manager, RMAN, backup & recover, and perfomance tuning. good luck.