Consider historical data showing that the average annual rate of return on the S&P 500 portfolio over the past 90 years has averaged roughly 8% more than the Treasury bill return, and that the S&P 500 standard deviation has been about 20% per year. Assume these values are representative of investors' expectations for future performance and that the current T-bill rate is 5%. a. Calculate the expected return and variance of portfolios invested in T-bills and the S&P 500 index with weights as follows: " Wills Windex 0 1.0 0.2 0.8 0.4 0.6 0.6 0.4 0.8 0.2 1.0 0 b. Calculate the utility levels of each portfolio of Problem a for an investor with A-2. What do you conclude? c. Repeat Problem b for an investor with A-3. What do you conclude? Vou manage ariel nortfolio with and ente 100/