3.56

Speeding linked to fatal car crashes. According to the National Highway Traffic and Safety Administration’s National Center for Statistics and Analysis (NCSA), “speeding is one of the most prevalent factors contributing to fatal traffic crashes” (NHTSA Technical Report, Aug. 2005). The probability that speeding is a cause of a fatal crash is .3. Furthermore, the probability that speeding and missing a curve are causes of a fatal crash is .12. Given speeding is a cause of a fatal crash, what is the probability that the crash occurred on a curve?

3.61

Internet user study. In a study of Internet users, researchers discovered that 80% of the users own at least one computer and that 25% of the users log on to the Internet for more than 30 hours per week (Internet Research, Vol. 11, 2001). Suppose that 15% of the users own at least one computer and log on to the Internet for more than 30 hours per week.

a) Given an Internet user owns at least one computer, what is the probability that he or she logs on to the Internet for more than 30 hours per week?

b) Given an Internet user logs on to the Internet for more than 30 hours per week, what is the probability that he or she owns at least one computer?