Chebyshev's theorem states that for a large class of distributions, no more than 1/k² of the distribution will be k standard deviations away from the mean.
This means that 1 - 1/k² of the distribution will be within k standard deviations from the mean.
Because k = 1.8, the amount of the distribution that is within 1.8 standard deviations from the mean is 1 - 1/1.8² = 0.6914 = 69.14%
