Which set correctly lists the approximate percentages of data within 1, 2, and 3 standard deviations of the mean in a normal distribution?

• A. 60%, 90%, 95%
• B. 70%, 95%, 99%
• C. 68%, 95%, 99%
• D. 65%, 92%, 98%

Answer: (C)

In a normal distribution, most data cluster around the mean, and the empirical rule describes how much falls within each distance from the mean: about 68% within one standard deviation, about 95% within two standard deviations, and about 99.7% within three standard deviations. Therefore, the set that lists 68% for within one standard deviation, 95% for within two, and 99% (rounded from 99.7%) for within three is the best match. The other options don’t align with these well-known percentages—they either underestimate or overestimate at one or more of the ranges.