Suppose the specialty food chain from Exercise 26 wants to now compare the change in sales across different regions. An examination of the difference in sales over a 37-week period in a recent year for 8 stores in the state of Massachusetts compared to 12 stores in nearby states reveals the following descriptive statistics for relative increase in sales. (If these means are multiplied by 100, they show % increase in sales.)

a) Find the 90% confidence interval for the difference in relative increase in sales over this time period.
b) Is there a significant difference in increase in sales between these two groups of stores? Explain.
c) What would you like to see to check the conditions?

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State N MA Other 12 0.0559 0.0503 Mean 0.0738 StDev 0.0666