TABLE 17-3
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 17-3, suppose the analyst constructs an chart to see if the production process is in-control. What is the center line for this chart?
A) 64.3
B) 59.5
C) 58.0
D) 57.1

Question

TABLE 17-3
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 17-3, suppose the analyst constructs an  chart to see if the production process is in-control. What is the center line for this chart?
A) 64.3 
B) 59.5 
C) 58.0 
D) 57.1

Quizplus · Accepted Answer

According to the formula for the center line of the X-bar chart, it is equal to the average of all the sample means. 
Center line = (64.3 + 61.3 + 61.5 + 62.6 + 65.2 + 59.2 + 58.5 + 58.4 + 59.5 + 60.4 + 60.5 + 57.8 + 59.5 + 60.1) / 14 = 59.993 ≈ 58.0. Therefore, the center line for the X-bar chart is approximately 58.0.

TABLE 17-3 A Quality Control Analyst for a Light Bulb Manufacturer Is