Probability

Probability is the mathematical chance that a certain even will occur out of a number of various possible events. Probability is represented as a number between 0 (representing impossibility), and 1 (representing certainty). Sometimes percentages are used, with numbers from 0% to 100%.

The letter P is used to indicate the probability of some event. For example P(heads) could represent the probability of tossing heads on a coin. More generally, probability can be described in terms of events. These relate to set theory in the following way. The sample space S can be thought of as the set of all possible outcomes. P(S) = 1, as it is certain that one outcome must occur. An event can be thought of as a subset of S. For example, heads would be the subset of the outcomes where heads is tossed on a coin.