Instruction 18-9
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 Instruction 18-9,suppose the sample mean and range data were based on 11 observations per day instead of 10.How would this change affect the lower and upper control limits of the R chart?
A)Both LCL and UCL would remain the same.
B)LCL would remain the same;UCL would decrease.
C)LCL would increase;UCL would decrease.
D)LCL would decrease;UCL would increase.

Question

Quizplus · Accepted Answer

The calculation of the lower and upper control limits of the R chart depends on the number of samples taken per day. Increasing the number of observations per day from 10 to 11 would result in a decrease in the R-chart's lower and upper control limits. The new limits would be:

LCL = D3(R-bar)
UCL = D4(R-bar)

Where D3 and D4 are constants based on the number of observations per day, and R-bar is the average range of the 11 observations. Since increasing the number of observations per day leads to a smaller R-bar, the control limits decrease as well. Therefore, choice C is correct.

Instruction 18-9 A Quality Control Analyst for a Light Bulb Manufacturer Is