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: 
What is the standard deviation of the sampling distribution of sample means?
A) 5 hours
B) 6.67 hours
C) 10 hours
D) 11.55 hours
E) 20 hours
Correct Answer:
Verified
Correct Answer:
Verified
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