The report New Study Shows Need for Americans to Focus
The report “New Study Shows Need for Americans to Focus on Securing Online Accounts and Backing up Critical Data” (PRNewswire, October 29, 2009) reported that only 25% of Americans change computer passwords quarterly, in spite of a recommendation from the National Cyber Security Alliance that passwords be changed at least once every 90 days. For purposes of this exercise, assume that the 25% figure is correct for the population of adult Americans.
a. If a random sample of 20 adult Americans is selected, what is the probability that exactly 3 of them change passwords quarterly?
b. What is the probability that more than 8 people in a random sample of 20 adult Americans change passwords quarterly?
c. What is the mean and standard deviation of the variable x = number of people in a random sample of 100 adult Americans who change passwords quarterly?
d. Find the approximate probability that the number of people who change passwords quarterly in a random sample of 100 adult Americans is less than 20.
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