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In a standard normal distribution, what percent of values lie within ±1 standard deviation of the mean?
A50%
B99.7%
C95%
D68%
Answer & Solution
Correct answer: D. 68%
1. Empirical (68-95-99.7) rule for Normal distributions.
2. About 68% within ±1σ, 95% within ±2σ, 99.7% within ±3σ.
3. Used heavily in process control and quality assurance.
4. Hence (B) is correct.
_Source: Maharashtra Balbharati Std XII Mathematics & Statistics (Commerce), Ch 8 "Probability Distributions", §8.3 ¶§8.3_
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