Question

So this is what I got as my Standard Deviation after plugging in the numbers:

A supermarket chain wants to know if their "buy one, get one free" campaign increases customer traffic enough to justify the cost of the program. For each of 10 stores they select two days at random to run the test. For one of those days (selected by a coin flip), the program will be in effect. They want to test the hypothesis that there is no mean difference in traffic against the alternative that the program increases the mean traffic. The accompanying table shows the number of customer visits to each of the 10 stores. Complete parts a through i below EB Click the icon to view the data table 1 Data Table b) Find the mean difference. That is, the mean of the pairwise differences (With Program - Without Program) Without Program 140 232 112 46 321 139 122 35 179 144 Store # With Program d1.60 Round to two decimal places as needed.) 145 231 105 c) Compute the standard deviation of the differences 4 325 135 124 29 192 145 Round to two decimal places as needed.) Enter your answer in the answer box and then click Check Answer 10 Clear All remaining

So I Subtracted the two Standard Deviations (85.36-83.83)=1.53, but that is not the answer apparently. What am I doing wrong?

Answer 1