22. The article The Foreman s View of Quality Control

(Quality Engrg., 1990: 257—280) described an investigation into the coating weights for large pipes resulting from a galvanized coating process. Production standards call for a true average weight of 200 lb per pipe. The accompanying descriptive summary and boxplot are from MINITAB.

Variable N Mean Median TrMean StDev SEMean ctg wt 30 206.73 206.00 206.81 6.35 1.16 Variable Min Max Q1 Q3 ctg wt 193.00 218.00 202.75 212.00

a. What does the boxplot suggest about the status of the speci cation for true average coating weight?

b. A normal probability plot of the data was quite straight. Use the descriptive output to test the appropriate hypotheses.