Asset A will generate a $20\%$ return with probability $0\mathrm{.}25$ ; a $15\%$ return with probability $0\mathrm{.}50$ ; and a $-15\%$ return with probability $0\mathrm{.}25.$ The standard deviation of the return on Asset $A$ is $\%.$

Write your answer as a percentage, rounded to $2$ decimal places. Example: if the answer is $10\mathrm{.}3478\%,$ then write $"10\mathrm{.}35".$ Do not type the $\%$ sign in your answer.