The National Quality Research Center at the University of Michigan provides a quarterly measure of consumer opinions about products and services (The Wall Street Journal, February 18, 2003). A survey of 10 restaurants in the Fast Food/Pizza group showed a sample mean customer satisfaction index of 71. Past data indicate that the population standard deviation of the index has been relatively

stable with σ = 5

a. What assumption should the researcher be willing to make if a margin of error is desired?

b. Using 95% confidence, what is the margin of error?

c. What is the margin of error if 99% confidence is desired?