is a quantified measure of the likelihood that an event will occur. The probability of an event is always a value between 0 and 1. Probability Vocabulary a group of outcomes with something in commone The set of every possible outcome/event (very general)+ A particular event or outcome (very specific)+ The total number of events in the sample space (5). The total number of times the event A can occur. The complement of event A, is the event that "event A does not happen"+ A' is called "A prime" or "not A". A is called "tilda A"+ Probability of event A: t t For a particular event A, P(A) is 0