A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his company produces. He knows from numerous previous samples that when this service life is in control it is normally distributed with a mean of 500 hours and a standard deviation of 20 hours. On three recent production batches, he tested service life on random samples of four headlamps, with these results

Sample	Service Life (hours)
1	495	500	505	500
2	525	515	505	515
3	470	480	460	470

What is the mean of the sampling distribution of sample means when the service life is in control?

Group of answer choices

250 hours

470 hours

495 hours

500 hours

515 hours

A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results

Machine	Measurements
#1	17	15	15	17
#2	16	25	18	25
#3	23	24	23	22

What is the sample mean for machine #1?

Group of answer choices

15

16

17

21

23

A quality analyst wants to construct a control chart for determining whether three machines, all producing the same product, are in control with regard to a particular quality variable. Accordingly, he sampled four units of output from each machine, with the following results

Machine	Measurements
#1	17	15	15	17
#2	16	26	18	25
#3	23	25	23	22

What is the estimate of the sample average range based upon this limited sample?

Group of answer choices

10

5.4

4.333

5

20