Question

A student wants to compare textbook prices for two online bookstores. She takes a random sample of five textbook titles from a list provided by her college bookstore, and then she determines the prices of those textbooks at each of the two websites. The prices of the five textbooks selected are listed below in the same order for each online bookstore.

A.com: $115, $43, $99, $80, $119

B.com: $110, $40, $99, $69, $109

(a) Are these independent or dependent samples?

Independent. The same textbooks are being compared.Dependent. The same textbooks are being compared.    Independent. Different textbooks are being compared.Dependent. Different textbooks are being compared.

(b) To construct a confidence interval, conditions for the data must be checked. Which variable should be checked?

the difference between the textbook price from A.com and the textbook price from B.com for each textbook.the prices of textbooks from B.com    the prices of textbooks from A.comthe difference between the average textbook price for A.com and the average textbook price for B.com

(c) Find a 94% confidence interval for the mean difference in textbook prices at the two online bookstores. (Use d = A.com - B.com.) HINT: Use StatCrunch. Enter the two columns of numbers, Stat > t stat > choose the appropriate test and fill in what's needed (   ,   ) (Use 3 decimal places)

(d) Suppose conditions are met. Using α = 0.06, is there evidence to indicate that the mean price of textbooks for A.com differs from the mean price of textbooks for B.com?

Because the interval does not contain zero, it is not plausible that the mean difference between A.com and B.com is 0. There is evidence to indicate that the mean price of textbooks for A.com is different from the mean price of textbooks for B.com .Because the interval contains zero, it is not plausible that the mean difference between A.com and B.com is 0. There is evidence to indicate that the mean price of textbooks for A.com is different from teh mean price of textbooks for B.com.    Because the interval does not contain zero, it is plausible that the mean difference between A.com and B.com is 0. There is not enough evidence to indicate that the mean price of textbooks for A.com is different from the mean price of textbooks for B.com.Because the interval contains zero, it is plausible that the mean difference between A.com and B.com is 0. There is not enough evidence to indicate that the mean price of textbooks for A.com differs from the mean price of textbooks for B.com.

Answer 1

Ans (a) Dependent. The same textbooks are being compared.

(b) To construct a confidence interval, conditions for the data must be checked. Which variable should be checked?

the difference between the textbook price from A.com and the textbook price from B.com for each textbook.

(c) using minitab>stat>basic stat>one sample t

we have

Paired T-Test and CI: A.com, B.com

Paired T for A.com - B.com

N Mean StDev SE Mean
A.com 5 91.2 31.0 13.9
B.com 5 85.4 30.3 13.6
Difference 5 5.80 4.66 2.08

94% CI for mean difference: (0.380, 11.220)
T-Test of mean difference = 0 (vs ≠ 0): T-Value = 2.78 P-Value = 0.050

a 94% confidence interval for the mean difference in textbook prices at the two online bookstores is (0.380, 11.220)
(d) Because the interval does not contain zero, it is not plausible that the mean difference between A.com and B.com is 0. There is evidence to indicate that the mean price of textbooks for A.com is different from the mean price of textbooks for B.com