A First Course in Statistics, 12th Edition

3.2 Unions and Intersections

An event can often be viewed as a composition of two or more other events. Such events, which are called compound events, can be formed (composed) in two ways.

The union of two events A and B is the event that occurs if either A or B (or both) occurs on a single performance of the experiment. We denote the union of events A and B by the symbol $A\cup B.A\cup B$ consists of all the sample points that belong to A or B or both. (See Figure 3.7a.)

Figure 3.7

Venn diagrams for union and intersection

The intersection of two events A and B is the event that occurs if both A and B occur on a single performance of the experiment. ...