The dollar value of orders placed through a particular store catalog is found to be normally distributed with a standard deviation of $21.58. A sample of 30 orders averaged $81.25. What is the 90% confidence interval around this sample mean?
A)	$81.25 $21.58
B)	$81.25 $10.79
C)	$81.25 $12.15
D)	$81.25 $6.48
Answer:D
The dollar value of orders placed through a particular store catalog is found to be normally distributed with a standard deviation of $21.58. A sample of 30 orders averaged $81.25. What is the 90% confidence interval around this sample mean?
A)	$81.25 $21.58 B)	$81.25 $10.79 C)	$81.25 $12.15 D)	$81.25 $6.48