The article “The Foreman’s View of Quality Control”

(Quality Engr., 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 n 5 25, t 5 23.9 n 5 25, t 5 22.6, a 5 .01 n 5 13, t 5 21.6, a 5 .05 n 5 13, t 5 1.6, a 5 .05 190 200 210 220 Coating weight

a. What does the boxplot suggest about the status of the specification 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.