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 Stock y Stock z Boom .04 .17 .09 .09 Normal .81 .08 .06 .08 Recession .15 − .24 .02 − .13 1. 7.72 percent 2. 6.31 percent 3. 7.38 percent 4. 6.49 percent 5. 5.65 percent