Theoretical Distribution

Concept:The interval $(\mu - 3\sigma, \mu + 3\sigma)$ in a normal distribution covers almost the entire area under the curve, leaving only a tiny fraction outside.Explanation:In a normal distribution, the empirical rule states that about $68\%$ of the area lies within $1\sigma$, $95\%$ within $2\sigma$, and $99.7\%$ within $3\sigma$. More precisely, for a standard normal curve, the area between $z = -3$ and $z = +3$ is $0.9973$ (i.e., $99.73\%$). Thus, the area outside this interval is $1 - 0.9973 = 0.0027$, which is $0.27\%$. Therefore, the interval $(\mu - 3\sigma, \mu + 3\sigma)$ covers all but $0.27\%$ of the area.Answer:D. all but $0.27\%$ area of a normal distribution.