An investor can design a risky portfolio based on two stocks, a and b. stock a has an expected return of 21% and a standard deviation of return of 39%. stock b has an expected return of 14% and a standard deviation of return of 20%. the correlation coefficient between the returns of a and b is .4. the risk-free rate of return is 5%. the standard deviation of returns on the optimal risky portfolio is 25.5%