For a skewed distribution that has excess kurtosis, the minimum percentage of the distribution within three standard deviations of the mean is closest to:

Chebyshev's inequality holds regardless of the shape of the distribution. For any k > 1, the minimum percentage of the distribution within k standard deviations of the mean is 1 − 1/k . Thus, for 3 standard deviations, the percentage is ≥ 1 − 1/9 = 89%.