what is the approximate percentage of lightbulb replacement requests numbering between 35 and 62

Question

The physical plant at the main campus of a large state university recieves daily requests to replace florecent lightbulbs. The distribution of the number of daily requests is bell-shaped and has a mean of 62 and a standard deviation of 9. Using the 68-95-99.7 rule,

Answer 1

Since it's a bell-shaped curve, we know that approx. 99.7% of the observation lies within three std, deviations (9 in this case) of the mean. With a mean=62, we expect 99.7% to be between 35 and 89, but we're only interested in those between 35 and 62. Since we have bell shaped curve, we're also assuming it's symmetrical, and we're only interested in the bottom half of that interval, so divide the probability by 2:

99.7/2=49.85%, and that's the answer to your problem!