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About 99.7 percent of the values of a normal distribution fall within how many standard deviations of the mean?
AOne of them
BTwo of them
CFour of them
DThree of them
Answer & Solution
Correct answer: D. Three of them
1. The empirical rule pairs each distance with a share of the values.
2. One standard deviation covers about 68 percent.
3. Two standard deviations cover about 95 percent.
4. Three standard deviations cover about 99.7 percent, so almost every value lies inside.
_Source: OpenStax High School Statistics (CC BY 4.0), section 6.1 The Standard Normal Distribution_
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