평균. Mean

산술평균 (arithmetic mean)

$$ \overline{x} = \frac{1}{n} \sum_{i=1}^n x_i $$

기하평균 (geometric mean)

$$ \overline{x} = \sqrt[n]{ \prod_{i=1}^n x_i } $$

조화평균 (harmonic mean)

$$ \overline{x} = \frac{n}{ \sum_{i=1}^n \frac{1}{x_i} } $$

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