"Probability Theory" is a branch of Math. It can get very, very complicated depending what the probability is. Example: If you toss a die(plural:dice) 11 times in a row, what is the probability that all 6 faces will turn up at least once? It turns out that this is extremely difficult to calculate accurately. You need advanced math to be able to solve it. You have to study "Probability Theory and Statistics" at university to be able to solve complicated probabilities.
