Question

Land's Bend sells 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 7 sales receipts for mail-order sales results in a mean sale amount of $81.70 with a standard deviation of $18.75. A random sample of 11 sales receipts for internet sales results in a mean sale amount of $74.60 with a standard deviation of $28.25. Using this data, find the 80% 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. Find the standard error of the sampling distribution to be used in constructing the confidence interval. Round your answer to two decimal places.

Answer 1

= [ (81.7 - 74.6) 1.337 × 11.0804 ]

= ( 7.1 14.81 )

= ( -7.71 , 21.91 )