A National Retail Foundation survey found households intended to spend an average of $649 during the December holiday season (The Wall Street Journal, December 2, 2005). Assume that the survey included 600 households and that the sample standard deviation was $175.
a. With 95% confidence, determine the margin of error.
b. Determine the 95% confidence interval estimate of the population mean
c. The prior year, the population mean expenditure per household was $632. Discuss the change in holiday season expenditures over the one-year period.