Question

Eddie Clauer 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 $64.90 with a standard deviation of $18.75. A random sample of 11 sales receipts for internet sales results in a mean sale amount of $83.10 with a standard deviation of $27.25. 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.

Step 3 of 3 :  

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

Lower endpoint: ___________ Upper endpoint: _____________

Answer 1

The 90% confidence interval for two means is, (8-5)-»**<-4 <8–5)= At 90% confidence level with 6 degrees of freedom is, 19=1943 Substitute the values is the above equation, that is, (5-3) JS1+2 <-1, < (51-53)+ + 12 (64.90–83.10) -1.943,(18.75), (27,25) < 44–<(64.90-83.10) +1.943, (18.75)*_ (27.25)* -18.2-21.0821<4-lly <-182+21.0821 -39.28 < 14-17 < 2.88 Lower endpoint = -39.28 Upper endpoint = 2.88