QUESTION 30

1. 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: Compute the Upper Control Limit for the Mean chart

   Sample	Service Life (hours)
   1	490	500	500	500
   2	520	515	530	515
   3	475	480	490	470

   		510 hours
   		470 hours
   		485 hours
   		500 hours
   		515 hours