According to Internet security experts, approximately 90% of all e-mail messages are spam (unsolicited commercial e-mail), while the remaining 10% are legitimate.
A system administrator wishes to see if the same percentages hold true for the e-mail traffic on her servers. She randomly selects e-mail messages and checks to see whether or not each one is legitimate. (Unless otherwise specified, round all probabilities below to four decimal places.)
Assuming that 90% of the messages on these servers are also spam, compute the probability that the first legitimate e-mail she finds is the seventh message she checks.
Compute the probability that the first legitimate e-mail she finds is the seventh or eighth message she checks.
Compute the probability that the first legitimate e-mail she finds is among the first seven messages she checks.
On average, how many messages should she expect to check before she finds a legitimate e-mail?
REALLY CONFUSED. DONT KNOW WHERE TO START.
I BELIEVE THIS IS GEOMETRIC DISTRIBUTION.
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