Question

Eddie Clauersells a wide variety of outdoor equipment and clothing. The company sells both through mail order and via the internet. Random samples of sales receipts were studied for mail-order sales and internet sales, with the total purchase being recorded for each sale. A random sample of 11sales receipts for mail-order sales results in a mean sale amount of $81.20with a standard deviation of $23.75. A random sample of 19sales receipts for internet sales results in a mean sale amount of $98.00with a standarddeviation of $25.25. Using this data, find the 90%confidence interval for the true mean difference between the mean amount of mail-order purchases and the mean amount of internet purchases. Assume that the population variances are not equal and that the two populations are normally distributed. (8 points)

Step 1. Find the point estimate that should be used in constructing the confidence interval.

2. Find the margin of error to be used in constructing the confidence interval. Round your answer to six decimal places.Answer: ____________________

Step 3. Construct the 90%confidence interval. Round your answers to two decimal places.

Answer 1

The statistical software output for this problem is:

From above output:

1) Point estimate = -16.8

2) Margin of error = (-0.98760084 + 32.612399)/2 = 15.812399

3) Lower bound = -32.61

Upper bound = -0.99