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 this service life 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
1. What is the mean of the sampling distribution of sample means when service life is in control?A. 250 hours
B. 470 hours
C. 495 hours
D. 500 hours
E. 515 hours
2. If he uses upper and lower control limits of 520 and 480 hours, on what sample(s) (if any) does service life appear to be out of control?
A. sample 1
B. sample 2
C. sample 3
D. both samples 2 and 3
E. all samples are in control