Question:medium

In a Normal distribution, what percentage of data falls within two standard deviations of the mean?

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Remember the \textbf{68–95–99.7 rule} for Normal distribution: \[ 1\sigma \rightarrow 68%, \qquad 2\sigma \rightarrow 95%, \qquad 3\sigma \rightarrow 99.7% \] It is frequently used in statistics and data analysis.
Updated On: Mar 16, 2026
  • \(68%\)
  • \(95%\)
  • \(99.7%\)
  • \(90%\)
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Understanding the Question
The question asks for the proportion of data in a Normal distribution that lies in the interval from two standard deviations below the mean to two standard deviations above the mean, i.e., \( (\mu - 2\sigma, \mu + 2\sigma) \).
Step 2: Key Formula or Approach
This question relates to the Empirical Rule, also known as the 68–95–99.7 rule, which is a key property of the Normal distribution.
Step 3: Detailed Explanation
The Empirical Rule states the approximate percentage of data within certain ranges around the mean (\(\mu\)) for a Normal distribution with standard deviation (\(\sigma\)):

Approximately 68% of the data falls within one standard deviation of the mean (\(\mu \pm \sigma\)).

Approximately 95% of the data falls within two standard deviations of the mean (\(\mu \pm 2\sigma\)).

Approximately 99.7% of the data falls within three standard deviations of the mean (\(\mu \pm 3\sigma\)).

The question specifically asks for the percentage within two standard deviations.
Step 4: Final Answer
According to the Empirical Rule, approximately 95% of the data falls within two standard deviations of the mean.
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