A design engineer wants to construct a sample mean chart for controlling the service life of a halogen headlamp his compary prodices, He knows from numerous previous samples that this service life is normally distributed with a mean of 500 hours and a staridard deviation of 20 hours, On threa racent broduction batches. he tested service life on random samples of four headlamps, with these result: If he uses upper and lower control limits of 520 and 480 hours, on what samplein (if any) does service ife appelar fo be cut af controf sample 1 sampie 2 sample 3 both samples 2 and 3 all samples are in controf