EXAMPLE 4.24

Probability of at least three heads. Any event involving the number of heads observed can be expressed in terms of X, and its probability can be found from the distribution of X. For example, the probability of tossing at least three heads is

P(X ≥ 3) = 0.25 + 0.0625 = 0.3125

The probability of at least one head is most simply found by use of the complement rule: