During the past $6$ years, the stock of one of the firms listed on the Nairobi Securities exchange has moved as follows:

Year $201420152016201720182019$

Price $\%-15-1020251015$

What is the standard deviation of the return of the firm's stock?

Question $10$Select one:

$16\mathrm{.}71\%$

$36\mathrm{.}74\%$

$15\mathrm{.}00\%$

$40\mathrm{.}93\%$