- 例 1
- Listed below are the types and ages of four monkeys procured by a laboratory
for a drug trial.
Suppose two monkeys will be selected by lottery and assigned to an experimental drug. Considering all possible choices of two monkeys, make a Venn digram and show the following events.

Here the elementary outcomes are the possible choices of a pair of numbers from . These pairs are listed and labeled as

*e*_{1},*e*_{2},*e*_{3},*e*_{4},*e*_{5},*e*_{6}for ease of reference.

The pair hasboth monkeys of the same type, and so does the pair . Consequently, . Those with the same ages are , , and , so . And the diagram.

- 例 2
- Refer to the previous experiment of selectng two monkeys out of four. Let
,
,
,
Give the compositions of the events
The pairs consisting of different types are , , , and , so . The event is the same as the event

*C*. Employing the definitions of union and intersection, we obtain