1. For any event A: P (a) = 1-P (not a).

2. When events A and B satisfy that A is included in B: P(BnA)=P(B)-P(A), and P(A)≤P(B).

3. For any event A, P(A)≤ 1.

4. For any two events A and B, P(B-A)=P(B)-P(AB).

Verb (abbreviation of verb) (addition formula) For any two events A and B, P(A∪B)= P(A)+P(B)-P(A∪B).