I tried the entrance exam puzzles but they are just too hard! how can I get good enough to solve these puzzles and get in? I really feel I need some kind of mentor and I could benefit from a program like this.
https://github.com/rmu/mentoring
Keep trying the puzzles. If you are really stuck you can always look around GitHub for solutions written by other people, or jump in #rmu on freenode and ask for help. Of course you don't want to look at other people's solutions if you are applying for the core course, but asking for help with problem definitions is totally fine.
What you can definitely do (as Jordan mentioned) is get some help from our mentoring program. You'll be able to study at your own pace that way, but get some guidance as needed along the way: https://github.com/rmu/mentoring/wiki/Instructions-for-stude...