Normal Distribution -- Applicable to Winrates?

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No more than 1/k2 of the values are more than k standard deviations away from the mean

Equality holds exactly for any distribution that is a linear transformation of this one. Inequality holds for any distribution that is not a linear transformation of this one.

The theorem can be useful despite loose bounds because it applies to random variables of any distribution, and because these bounds can be calculated knowing no more about the distribution than the mean and variance.

Chebyshev's inequality is used for proving the weak law of large numbers.