As the number of air travelers with time on their hands increases, it would seem that spending on retail purchases in airports would increase as well.

A study by Airport Revenue News addressed the per person spending at selected airports for merchandise, excluding food, gifts, and news items. A file entitled Revenues contains sample data selected from airport retailers in 2005 and again in 2008.

a. Conduct a hypothesis test to determine if the average amount of retail spending by air travelers has increased as least as much as approximately

$0.10 a year from 2005 to 2008. Use a significance level of 0.025.

b. Using the appropriate analysis (that of part a or other appropriate methodology), substantiate the statement that average retail purchases in airports increased over the time period between 2005 and 2008. Support your assertions.

c. Parts a and b give what seems to be a mixed message. Is there a way to determine what values are plausible for the difference between the average revenue in 2005 and 2008? If so, conduct the appropriate procedure.