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