Probability Rules

Question 1

Conditional Probability of B given A

Answer 1

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

Question 2

Independence (formal)

Answer 2

Events A and B are independent if:

P(B|A) = P(B)

Question 3

General Addition Rule

Answer 3

For any two events, A and B, the probability of A or B is

P(A or B) = P(A) + P(B) - P(A and B)

Question 4

General Multiplication Rule

Answer 4

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

Question 5

Tree Diagram

Answer 5

A display of conditional events or probabilities that is helpful in thinking through conditioning.

Question 6

Bayes’ Rule
P(A|B)=

Answer 6

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