Assume that the economy has an $40\%$ chance of booming, a $38\%$ chance of being normal, and being recessionary the remainder of the time. A stock is expected to return $22\mathrm{.}13\%$ in a boom economy, $15\mathrm{.}83\%$ in a normal economy, and $-15\mathrm{.}63\%$ in a recession economy. What is the standard deviation of returns on the stock?