Assignment:
Assume that the two samples are independent simple random samples selected from normally distributed populations. Do not assume that the population standard deviations are equal, unless your instructor stipulates otherwise.
Confidence Interval for Checks and Charges Refer to the sample data given in Exercise and construct a 90% confidence interval for the difference between the mean of the cents portions from checks and the mean of the cents portions from credit card charges. What does the confidence interval suggest about the means of those amounts?
Exercise
Hypothesis Test for Checks and Charges The author collected a simple random sample of the cents portions from 100 checks and from 100 credit card charges. The cents portions of the checks have a mean of 23.8 cents and a standard deviation of 32.0 cents. The cents portions of the credit charges have a mean of 47.6 cents and a standard deviation of 33.5 cents. Use a 0.05 significance level to test the claim that the cents portions of the check amounts have a mean that is less than the mean of the cents portions of the credit card charges. Give one reason that might explain a difference.