# Question

For the purchase amounts in Exercise 8:

a) Construct a 90% confidence interval for the mean purchases of all customers, assuming that the assumptions and conditions for the confidence interval have been met.

b) How large is the margin of error?

c) How would the confidence interval change if you had assumed that the standard deviation was known to be $20?

a) Construct a 90% confidence interval for the mean purchases of all customers, assuming that the assumptions and conditions for the confidence interval have been met.

b) How large is the margin of error?

c) How would the confidence interval change if you had assumed that the standard deviation was known to be $20?

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