EXAMPLE 4.48

Conditional versus unconditional probabilities. In the notation of Example 4.47, this is the conditional probability P(A₁ | C). Start from the definition of conditional probability and then apply the results of Example 4.47:

More than half of adult chat room participants are between 18 and 29 years old. Compare this conditional probability with the original information (unconditional) that 29% of adult Internet users are between 18 and 29 years old. Knowing that a person chats increases the probability that he or she is young.