# statistics

The physical plant at the main campus of a large state university receives daily requests to replace florecent lightbulbs. The distribution of the number of daily requests is bell-shaped and has a mean of 37 and a standard deviation of 3. Using the empirical rule (as presented in the book), what is the approximate percentage of lightbulb replacement requests numbering between 37 and 40?

Do not enter the percent symbol.

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1. Don't know what book says, but this is another way.

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z scores.
Multiply by 100.

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2. Is this your book's rule?

Do you know the 68-95-99.7 rule? Approximately 68% of scores in normal distribution are within one standard deviation (34% on each side of the mean), 95% within 2 SD, and 99.7% within 3 SD.

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