Probability of an Event

In probability theory, an event is a set of outcomes of an experiment, to which a probability is assigned. A single outcome may be an element of many different events, and different events in an experiment are usually not equally likely, since they may include very different groups of outcomes. In words, this means that the probability of an event must be a number between 0 and 1(inclusive). Also, probability of an impossible event is always zero. On the other hand, the probability of an impossible event is always zero.