A pharmaceutical manufacturer purchases a particular material from two different suppliers. The mean level of impurities in the raw material is approximately the same for both suppliers, but the manufacturer is concerned about the variability of the impurities from shipment to shipment. To compare the variation in percentage impurities for the two suppliers, the manufacturer selects 10 shipments from each of the two suppliers and measures the percentage of impurities in the raw material for each shipment. The sample means and variances are shown in the table.

a. Do the data provide sufficient evidence to indicate a difference in the variability of the shipment impurity levels for the two suppliers? Test using α = .01. Based on the results of your test, what recommendation would you make to the pharmaceutical manufacturer?
b. Find a 99% confidence interval for σ22 and interpret your results.

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Supplier ASupplier B 11.89 X21.85 s 273 - 094 10 n2-10