Download Chapter 10 - Hampden

Probability rules (cont'd)
5) Two events A and B are independent knowing that one event
occurred doesn’t affect the probability that the other occurs. If A and B
are independent, the probability that both A and B occurs is the product
of their individual probabilities.
P(A and B) = “P(A B)” = P(A) P(B)
This is the multiplication rule for independent events.
Example: Flip a fair coin twice. The coin has no “memory”, so the outcome of
the first flip can’t affect the probabilities for the second flip. The first and
second flips are independent.
Let A = {toss 1 is heads}, B = {toss 2 is tails}. Then
P(A and B) = P(HT) = P(H) P(T) = 0.5 + 0.5 = 0.25