The probability of coming out ahead in a european roulette Suppose I've bring 500 dollar to a roulette game, and spend 5$ every spin placing on a corner(4/37 winning), what's my chance to coming out ahead after 89 spins? what about 91 spins?

Technically, you never specified when you stopped playing, and if you keep playing until you cant (you run out of money) then you have a 100% chance of losing your money if you keep playing indefinitely. Probably not the answer you are looking for, but the mathematically correct one to your question.
