A design engineer wants to construct a sample mean chart for controlling the ser

Question

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:

What is the sample mean service life for sample 2?

Explanation / Answer

Sample mean service life of sample 2

= (Sum of obervations in sample 2) / (Number of observations in sample 2)

Here,

Sum of observations = 494 + 493 + 510 + 501 = 1998

Number of observations = 4

So,

Mean service life of sample 2

= 1998 / 4

= 499.5

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