สถิติ - ความแปรปรวน

${ \delta = \frac{ \sum (M - n_i)^2 }{n}}$

${ M = \frac{600 + 470 + 170 + 430 + 300}{5} \\[7pt] = \frac{1970}{5} \\[7pt] = 394}$

${ \delta = \frac{ \sum (M - n_i)^2 }{n} \\[7pt] = \frac{(600 - 394)^2 + (470 - 394)^2 + (170 - 394)^2 + (430 - 394)^2 + (300 - 394)^2}{5} \\[7pt] = \frac{(206)^2 + (76)^2 + (-224)^2 + (36)^2 + (-94)^2}{5} \\[7pt] = \frac{ 42,436 + 5,776 + 50,176 + 1,296 + 8,836}{5} \\[7pt] = \frac{ 108,520}{5} \\[7pt] = \frac{(14)(13)(3)(11)}{(2)(1)} \\[7pt] = 21,704}$