Probability Rules Part 1

General Addition Formula

• P(AUB)= P(A) + P(B) - P(A∩B)

• P(AUB, but not both)= P(A) + P(B)-2P(A∩B)

Contingency table and Venn diagrams

Ways to visually display data for probability

Conditional Probability

When we want to know the probability of an event after we know that another event has already happened

Conditional Probability Formula

P(B|A)= P(A∩B)/P(A)

Make sure you know which event is given for conditional probability because..

P(A|B) is NOT the same as P(B|A)

Independence formula

P(B|A)=P(B) (the probability that B happens is the same whether or not A happens)