A consumer advocate researches the length of life between two brands of refrigerators, Brand A and Brand B. He collects data on the longevity of 40 refrigerators for Brand A and repeats the sampling for Brand B. A portion of the data is shown in the accompanying table; the full data set is on the text website, labeled Refrigerator Longevity.
![884_labeled Refrigerator Longevity.png](https://secure.tutorsglobe.com/CMSImages/884_labeled Refrigerator Longevity.png)
a. Specify the competing hypotheses to test whether the median length of life differs between the two brands.
b. Calculate the value of the Wilcoxon rank-sum statistic W.
c. Assume that the sampling distribution of W is approximately normal; calculate the value of the test statistic Z.
d. With α = 0.05, does median longevity differ between the two brands? Explain.