Wait wait, am I the only here that sees that OP has no idea of probabilities? Your way of pulling 50/50 "either it exists or it does not" out of your ass and basing your whole argument on that is as hilarious as it is retarded. I am not even going to bother with the even more retarded division of this probability that follows.
If you are interested in a legitimate attempt to solve the problem of the existence of god via math then you should try Goedels theory or other ontological proof attempts. Granted, you won't understand them because your level of math is apparently very low.