Derive the standard deviation of the returns on a portfolio that is invested in stocks x, y, and z , where twenty percent of the portfolio is invested in stock x and 35 percent is invested in Stock z. State of Economy Probability of State of Economy Rate of Return if State Occurs Stock x .17 Stock z .09 .08 - .13 Boom Normal Recession O 1.6.31 percent .08 - .24 5.65 percent O 3.7.38 percent 0 4.6.49 percent 7.72 percent O 5.