15.74 Contaminants in Chemicals A man- ufacturer uses a large amount of a certain chem- ical. Since there are just two suppliers of this chemical, the manufacturer wishes to test whether the percentage of contaminants is the same for the two sources against the alternative that there is a difference in the percent- ages of contaminants for the two suppliers. Data from independent random samples are shown below:

a. Use the Wilcoxon rank sum test to determine whether there is a difference in the contaminant percentages for the two suppliers. Use a = 0.05.

b. Use the large-sample approximation to the Wil- coxon rank sum test to determine whether there is a difference in the contaminant percentages for the two suppliers. Use = 0.05. Compare your conclu- sions to the conclusions from part a.

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Supplier 1 2 0.86 0.65 0.55 0.58 0.69 1.13. 0.40 0.16 0.72 0.65 0.22 0.07 1.18 0.50 0.09. 0.36 0.45 1.04 0.16 0.20 1.41 0.41 0.26 0.15