What percentage of values lie within one standard deviation above and below the mean?

What percentage of values lie within one standard deviation above and below the mean?

• A. 50%
• B. 95%
• C. 68%
• D. 99%

Answer: (C)

In a normal distribution, about 68% of values lie within one standard deviation of the mean. This central band around the mean contains roughly two-thirds of the data because the curve is symmetric and the spread is defined by the standard deviation. The exact figure is about 68.27%. The remaining data sit in the tails beyond ±1 standard deviation, about 15.87% in each tail. The other percentages refer to wider ranges: about 95% within two standard deviations and about 99.7% within three standard deviations. If the data aren’t normally distributed, these exact percentages don’t necessarily hold.

In a normal distribution, about 68% of values lie within one standard deviation of the mean. This central band around the mean contains roughly two-thirds of the data because the curve is symmetric and the spread is defined by the standard deviation. The exact figure is about 68.27%. The remaining data sit in the tails beyond ±1 standard deviation, about 15.87% in each tail. The other percentages refer to wider ranges: about 95% within two standard deviations and about 99.7% within three standard deviations. If the data aren’t normally distributed, these exact percentages don’t necessarily hold.