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 42 and a standard deviation of 10. Using the empirical rule (as presented in the book), what is the approximate percentage of lightbulb replacement requests numbering between 22 and 42?

Answer 1

22 is two SD below the mean, in other words, Z = -2.

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 score and distance from the mean. Multiply by 100.