Probability Rules

Conditional Probability

Probability of Event A given that Event B has occured.

Conditional Probability Symbol

P(A|B)= P(A and B)/P(B)

Multiplication Rule

Intersection of two independent events (P(A and B)= P(A)+ P(B)) is equal to P(A) x P(B)

Addition Rule

Union of 2 events P(A or B)= P(A)+P(B)-P(A and B)

What does P(A or B) equal when events are mutually exclusive

0

Independence

Knowing whether one event occurs does not affect the probability that the other event occurs.

Compliment Rule

The probability of the Compliment of event A is equal to 1 minus the probability of event A

Compliments

All outcomes in the sample space that are not in event A

General Multiplication Rule

The probability of event A and B occuring is equal to the probability of event A given event B times the probability of event B.

3 ways to determine if events are independent

1. Is P(A|B)=P(A)

2. Is P(B|A) = P(B)

3. Is P(A and B)= P(A) times P(B)