A Design Engineer Wants to Construct a Sample Mean Chart

question 75

Multiple Choice

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: $$\begin{array} { c c c c c } \text { Sample } && { \text { Service Life (hours) } } \\\hline 1 & 495 & 500 & 505 & 500 \\2 & 525 & 515 & 505 & 515 \\3 & 470 & 480 & 460 & 470\end{array}$$
What is the standard deviation of the sampling distribution of sample means for whenever service life is in control?

• A) 5 hours
• B) 6.67 hours
• C) 10 hours
• D) 11.55 hours
• E) 20 hours

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