The Information Systems Audit and Control Association surveyed office workers to learn about the anticipated usage of office computers for personal holiday shopping (USA today, November 11, 2009). Assume that the number of hours a worker spends doing holiday shopping on an office computer follows an exponential distribution.

a. The study reported that there is a .53 probability that a worker uses an office computer for holiday shopping 5 hours or less. Is the mean time spent using an office computer for holiday shopping closest to 5.8, 6.2, 6.6, or 7 hours?

b. Using the mean time from part (a), what is the probability that a worker uses an office computer for holiday shopping more than 10 hours?

c. What is the probability that a worker uses an office computer for holiday shopping between 4 and 8 hours?