# Area under normal curve with 1 SD is –

Area under normal curve with 1 SD is –

**[A].** 0.34

**[B].** 0.68

**[C].** 0.17

**[D].** 0.12

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[A]. 0.34

**Explanation (Ref. Parks) –**

In a normal curve –

- The area between
**one standard deviation on either side of the mean**(x̄**±**1σ) will include approximately 68% of the values in the distribution, - The area between
**two standard deviations on either side of the mean**(x̄**±**2σ) will cover most of the values, i.e., approximately 95% of the values, and - The area between
**x̄ ± 3σ**will include 99.7% of the values.

These limits on either side of the mean are called “confident limits’.

**Note that**, in every sentence above, it’s clearly mentioned “… standard deviation on **either side** of mean …”, i.e. when ±** (+/-)** sign is given both sides are to be included for area calculation. However, the question which was asked was talking only about “1 SD”, i.e. **no ±** sign. So it would be treated as “+1 SD” only, therefore answer for the asked question would be 34% or **0.34** only (as shown in the diagram too).

Sorry. I may have marked it wrong. Yes, it should be 0.68, let me check it (tomorrow), and then will re-post the answer.

@Sanchi, I have updated my answer with explanation. I have taken reference from Park’s and PSM faculty. If you find any contradictory evidence to my note (written at the end of answer), please share it. Thanks.

Thank you.

Sir why not 0.68?