QUESTION 13 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: Service life in hours Sample 1 Sample 2 Sample 3 Sample 4 Observation 1 495 500 505 500 Observation 2 500 490 456 490 Observation 3 505 456 485 Observation 4 500 490 474 504 If he uses a LCL of 481 hours and an UCL of 503, on what sample(s) (if any) does service life appear to be out of control? Hint: you don't have to calculate the UCL or LC Sample 1 Sample 2 Sample 3 Sample 4 Sample 2 and 2