A manufacturer of headphones is interested in the sales of a particular headphone model in its stores in 8 airports. Some of these stores are located on the West and some on the East coast of the U.S. Also, the manufacturer recently conducted an advertising campaign. The sales before and after the advertising campaign, which it ran in February using billboards in the airports, are shown below (i.e., data for sales in those stores in January and data for sales in the same stores for March.) (Some descriptive statistics have also been provided in the table. You will need to decide which ones you need for your calculations in answering the questions below.)

Store Location Sales in Jan Sales in March Change in sales

1 East coast 190 220 30

2 East coast 205 250 45

3 East coast 220 255 35

4 East coast 240 265 25

5 West coast 123 160 37

6 West coast 129 140 11

7 West coast 100 120 20

8 West coast 140 160 20

Summary statistics

All stores Sales in Jan Sales in March Change in sales

Mean 168.38 196.25 22.88

SD 51.68 57.62 11.01

East Coast Sales in Jan Sales in March Change in sales

Mean 213.75 247.50 33.75

SD 21.36 19.36 8.54

West Coast Sales in Jan Sales in March Change in sales

Mean 123.00 145.00 22.00

SD 16.87 19.15 10.86

To get full points when answering each part below be sure to: calculate an appropriate statistic, state the result of the test, and state your conclusion.

a) Was there a difference in sales in January for stores on the East coast versus on the West coast?

b) Looking at all the stores, is there a difference in sales from January to March?

c) Did the campaign have a different effect on sales for stores on the East coast versus on the West coast? [6 points]