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The lifetimes of lightbulbs of a particular type are normally distributed with a mean of 400...

The lifetimes of lightbulbs of a particular type are normally distributed with a mean of 400 hours and a standard deviation of 10 hours. What percentage of the bulbs have lifetimes that lie within 2 standard deviations to either side of the mean? Use the Empirical Rule and write your answer as a percent rounded to 2 decimal places.

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solution

using empirical rule

P( - 2< X < + 2) = 95%

P(400 - 2 * 10 < X <400 + 2 * 10) = 95%

P(380 < X < 420) = 95%

Answer = 95%

orchestra answered 2 years ago
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