Exercises

1. The independent and normally distributed random variables X and Y have known standard deviations of img and img, respectively. A sample of 36 observations from the X population yielded img, and a sample of 49 observations from the Y population resulted in img. Using Equation (11.4), find a 99% confidence interval for the mean difference img.
2. The American Automobile Assn. (AAA) compared the mean prices per gallon of gasoline in two different metropolitan areas. The mean price per gallon in area X was img(nX = 40) and the mean price per gallon in area Y was img(nY = 35). If prior studies reveal that img and , find a 95% confidence interval for the mean difference . What assumptions are being made?

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