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

Question

Quizplus · Accepted Answer

The 90% confidence interval is calculated using the formula: mean ± (z-score * (standard deviation/√n)). For a 90% confidence level, the z-score is approximately 1.645. Thus, the interval is $81.25 ± (1.645 * (21.58/√30)) = $81.25 ± $6.48.

The Dollar Value of Orders Placed Through a Particular Store