Z = ± 1
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability between the Z scores. Multiply by 100.
The lifetimes of light bulbs of a particular type are normally distributed with a mean of 370 hours and a standard deviation of 5 hours. What percentage of bulbs has lifetimes that lie within 1 standard deviation of the mean on either side?
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