Chebyshev's inequality - Wikipedia
https://en.wikipedia.org/wiki/Chebyshev's_inequalityIn probability theory, Chebyshev's inequality (also called the Bienaymé–Chebyshev inequality) guarantees that, for a wide class of probability distributions, no more than a certain fraction of values can be more than a certain distance from the mean. Specifically, no more than 1/k of the distribution's values can be k or more standard deviationsaway from the mean (or equivalently, over 1 − 1/k of the distribution's values are less than k standard deviations away from the mean)…