Returns for the Cabell's Company over the last $3$ years are shown below. What's the standard deviation of

Cabell's returns? $($Hint: this is a historical data problem, not a probability distribution.$)$

$23\mathrm{.}87\%$

$22\mathrm{.}97\%$

$21\mathrm{.}79\%$

$25\mathrm{.}18\%$