In a standard normal distribution, approximately what percentage of data values lie within two standard deviations of the mean (between and )?
Answer and explanation
Correct answer: B. 95%
- Step 1: According to the empirical 68-95-99.7 rule for bell-shaped normal distributions:
- Step 2: Approximately 68% of data falls within 1 standard deviation ().
- Step 3: Approximately 95% falls within 2 standard deviations ().
- Step 4: Approximately 99.7% falls within 3 standard deviations ().
Answer
95%.
Why not the others: '68%' corresponds to 1 standard deviation; '90%' is the confidence interval bound for ; '99.7%' corresponds to 3 standard deviations.
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