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Find the percentage of the normal distribution by using z

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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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Hi there,

Here is my answer:

According to the question, z=+/-1 for those that lie within 1 standard ...

Solution Summary

For this solution, first we calculate the z scores. Then in the following step, we used z score based p value to calculate the probability.