A Design Engineer Wants to Construct a Sample Mean Chart

Multiple Choice

A design engineer wants to construct a sample mean chart for controlling the service life of one of the types of light bulbs 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 bulbs,with these results: 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.