Question:easy
In a normal curve, what is the area that comes under 1 standard deviation (mean +/- 1 SD)?
In a normal curve, what is the area that comes under 1 standard deviation (mean +/- 1 SD)?
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Remember the 68-95-99.7 rule for the normal curve.
Updated On: Jun 23, 2026
- 50%
- 68%
- 95%
- 100%
Show Solution
The Correct Option is B
Solution and Explanation
Step 1: Recall the fixed properties of a normal distribution, which are independent of the actual mean and SD values.
Step 2: The proportion of data within $k$ standard deviations follows the 68-95-99.7 rule: $\mu \pm 1\sigma \approx 68\%$, $\mu \pm 2\sigma \approx 95\%$, and $\mu \pm 3\sigma \approx 99.7\%$.
Step 3: Matching the asked limit of one standard deviation directly gives roughly two-thirds of all observations. \[\boxed{68\%}\]
Step 2: The proportion of data within $k$ standard deviations follows the 68-95-99.7 rule: $\mu \pm 1\sigma \approx 68\%$, $\mu \pm 2\sigma \approx 95\%$, and $\mu \pm 3\sigma \approx 99.7\%$.
Step 3: Matching the asked limit of one standard deviation directly gives roughly two-thirds of all observations. \[\boxed{68\%}\]
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