Returns for the Dayton Company over the last $3$ years are shown below. What's the standard deviation of the firm's returns? $($Hint: This is a sample, not a complete population, so the sample standard deviation formula should be used.$)$ Do not round your intermediate calculations.

Year

Return

$2013$

$21\mathrm{.}00\%$

$2012$

$-12\mathrm{.}50\%$

$2011$

$12\mathrm{.}50\%$

$$

$19\mathrm{.}33\%$

$15\mathrm{.}85\%$

$16\mathrm{.}37\%$

$21\mathrm{.}59\%$

$17\mathrm{.}41\%$