Key Concepts

• If two events are mutually exclusive, the addition rule for probability can be used to determine the probability of the outcome.
• If two events are not mutually exclusive, the addition rule for probability needs to be modified to determine the probability of the outcome.
• If two events are independent, the multiplication rule for probability can be used to determine the probability of the outcome.

Glossary

addition rule for probability: if $A$ and $B$ are any two mutually exclusive events, then $P(A \ \mathrm{OR} \ B) = P(A) + P(B)$. If $A$ and $B$ are NOT mutually exclusive events, then $P(A \ \mathrm{OR} \ B) = P(A) + P(B) - P(A \ \mathrm{and} \ B)$.

multiplication rule for probability: if $A$ and $B$ are independent events, then $P(A \ \mathrm{and} \ B) = P(A)P(B)$

sample space the set of all possible outcomes of an experiment