Basic Probability

The probability of an event A is: [formula] Probability is always between 0 and 1 (or 0% to 100%). - P(A) = 0: impossible - P(A) = 1: certain Complement: P(text{not } A) = 1 - P(A)

Example: A bag contains 4 red, 6 blue, and 5 green marbles. What is the probability of drawing a blue marble?

"OR" (Union): P(A text{ or } B) = P(A) + P(B) - P(A text{ and } B) If A and B are mutually exclusive (can't happen together): [formula] "AND" (Intersection): For independent events: [formula]

Example: A fair coin is flipped 3 times. What is the probability of getting all heads?