Posted by sally on Saturday, May 23, 2009 at 4:57pm.
The lifetimes of lightbulbs of a particular type are normally distributed with a mean of 290 hours
and a standard deviation of 6 hours. What percentage of the bulbs have lifetimes that lie within 1
standard deviation to either side of the mean?

Statistics  Ms. Sue, Saturday, May 23, 2009 at 5:00pm
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Statistics  PsyDAG, Sunday, May 24, 2009 at 12:28pm
Approximately 34% of scores lie between the mean and one standard deviation in any normal distribution. Therefore, μ ± 1 SD contains approximately 68% of the cases.
I hope this helps. Thanks for asking.
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