Data on the numbers of insured commercial banks in the United States during the period 1990-1996 are given in the file P3_69.XLS. 

a. Compare these seven distributions of the numbers of U.S. commercial banks. Do you find the mean and standard deviation of these numbers to be changing over time? If so, how do you explain the trends?

b. What trends do you notice in the numbers of commercial banks by region’? For example, how do the numbers of commercial banks appear to be changing in the northeastern United States over the given period? Summarize your findings for each region of the country.