Question: The article discussed in Problem also reported that the mean download time for the H&R Block Web site, www.hrblock.com, was 2.5 seconds. Suppose that the download time for the H&R Block Web site was normally distributed, with a standard deviation of 0.5 second. If you select a random sample of 30 download times,
a. what is the probability that the sample mean is less than 2.75 seconds?
b. what is the probability that the sample mean is between 2.70 and 2.90 seconds?
c. the probability is 80% that the sample mean is between what two values symmetrically distributed around the population mean?
d. the probability is 90% that the sample mean is less than what value?
Problem: The New York Times reported (L. J. Flynn, Tax Surfing, The New York Times, March 25, 2002, p. C10) that the mean time to download the home page for the Internal Revenue Service (IRS), www.irs.gov, was 0.8 second. Suppose that the download time was normally distributed, with a standard deviation of 0.2 second. If you select a random sample of 30 download times,
a. what is the probability that the sample mean is less than 0.75 second?
b. what is the probability that the sample mean is between 0.70 and 0.90 second?
c. the probability is 80% that the sample mean is between what two values, symmetrically distributed around the population mean?
d. the probability is 90% that the sample mean is less than what value?