TABLE 18-4
A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds)is too erratic and adversely affects expected profits.The supervisor proceeds by randomly sampling 5 individuals per hour for a period of 10 hours.The sample mean and range for each hour are listed below. She also decides that lower and upper specification limit for the critical-to-quality variable should be 10 and 30 seconds,respectively.
-Referring to Table 18-4,suppose the sample mean and range data were based on 6 observations per hour instead of 5.How would this change affect the lower and upper control limits of an R chart?
A)LCL would increase; UCL would decrease.
B)LCL would remain the same; UCL would decrease.
C)Both LCL and UCL would remain the same.
D)LCL would decrease; UCL would increase.

Question

TABLE 18-4
A factory supervisor is concerned that the time it takes workers to complete an important production task (measured in seconds)is too erratic and adversely affects expected profits.The supervisor proceeds by randomly sampling 5 individuals per hour for a period of 10 hours.The sample mean and range for each hour are listed below.  She also decides that lower and upper specification limit for the critical-to-quality variable should be 10 and 30 seconds,respectively.
-Referring to Table 18-4,suppose the sample mean and range data were based on 6 observations per hour instead of 5.How would this change affect the lower and upper control limits of an R chart?
A)LCL would increase; UCL would decrease. 
B)LCL would remain the same; UCL would decrease. 
C)Both LCL and UCL would remain the same. 
D)LCL would decrease; UCL would increase.

Quizplus · Accepted Answer

When the sample size increases, the control limits for an R chart become narrower, meaning the UCL decreases while the LCL remains the same because the LCL for an R chart is typically zero.

TABLE 18-4 A Factory Supervisor Is Concerned That the Time It Takes