alleryStart learning →About what percentage of values lie within three standard deviations of the mean?
A95 percent
B68 percent
C75 percent
D99.7 percent
Answer & Solution
Correct answer: D. 99.7 percent
1. Three standard deviations covers almost the whole distribution.
2. About 99.7 percent of the x values lie within three standard deviations of the mean.
3. The z-scores at those points are minus 2 and plus 2 for two deviations, and minus 3 and plus 3 for three.
4. Only about three values in a thousand fall outside that band.
_Source: OpenStax Introductory Statistics 2e (CC BY 4.0), Ch 6 'The Normal Distribution', sections 6.1-6.3_
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