5.17. The following data show daily averages of errors per truck over the daily production of about 125 trucks at final inspection. These data precede those of Table 5.3.

Day Total errors, c Average errors, u Day Total errors, c Average errors, u Nov 21 Th 156 1.25 Dec 5 Th 175 1.40 Nov 22 F 198 1.58 Dec 6 F 189 1.51 Nov 25 M 281 2.25 Dec 9 M 135 1.08 Nov 26 T 312 2.50 Dec 10 T 159 1.27 Nov 21 W 256 2.05 Dec 11 W 148 1.18 Nov 29 F 182 1.46 Dec 12 Th 174 1.39 Dec 2 M 192 1.54 Dec 13 F 178 1.42 Dec 3 T 178 1.42 Dec 16 M 260 2.08 Dec 4 W 196 1.57 Dec 17 T 231 1.85 3600 28.80

a. Plot the average errors per truck for the days.

b. Draw in control lines from the previous u-bar¼1.97 and comment.

c. Analyze these data as a preliminary run of data, checked for control.

d. Suggest a u-bar value for subsequent data.