14 Probability Summary

$P(A) = \frac{number\ of\ ways\ A\ can\ happen}{total\ number\ of\ possible\ outcomes}$

$P(A\ or\ B) = P(A) + P(B) - P(A \cap B)$

$P(A\ and\ B) = P(A) \times P(B) = P(A \cap B)$

Note: When $A$ and $B$ are mutually exclusive $P(A \cap B) = 0$