Reconsider Exercise 7.2.18 about rating bottled and tap water. 

a. Use the 2SD method to determine an approximate 95% confidence interval for the mean difference in water ratings (bottled – tap) for the population of interest. 

b. Based on your confidence interval, from part (a), is there strong evidence that the mean rating for bottled water is higher than that of tap water? Explain.

Data from Exercises 7.2.18

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Mean 0.000 SD 0.349 1.20 Exercise 7.2.18d 0.80 0.40 0.00 Average difference 0.40 0.80 1.20