TABLE 18-3
A quality control analyst for a light bulb manufacturer is concerned that the time it takes to produce a batch of light bulbs is too erratic.Accordingly,the analyst randomly surveys 10 production periods each day for 14 days and records the sample mean and range for each day.
-Referring to Table 18-3,suppose the analyst constructs an R chart to see if the variability in production times is in-control.What is the upper control limit for this R chart?
A)10.66
B)9.37
C)7.98
D)6.34

Question

TABLE 18-3
A quality control analyst for a light bulb manufacturer is concerned that the time it takes to produce a batch of light bulbs is too erratic.Accordingly,the analyst randomly surveys 10 production periods each day for 14 days and records the sample mean and range for each day. 
-Referring to Table 18-3,suppose the analyst constructs an R chart to see if the variability in production times is in-control.What is the upper control limit for this R chart?
A)10.66 
B)9.37 
C)7.98 
D)6.34

Quizplus · Accepted Answer

The upper control limit for an R chart is calculated as D4 * Rbar, where D4 is a constant that depends on the sample size and Rbar is the average range of the sample. For a sample size of 5, D4 = 2.114. The average range can be calculated as the average of the ranges of the samples. From Table 18-3, the ranges of the samples are 6, 8, 10, 12, and 14. The average range is (6 + 8 + 10 + 12 + 14) / 5 = 10. Therefore, the upper control limit for the R chart is 2.114 * 10 = 21.14.

TABLE 18-3 A Quality Control Analyst for a Light Bulb Manufacturer Is