1. The S&P 500 index delivered a return of 20%, -10%, 25%, and 5% over four successive years. What is the arithmetic average annual return per year?

2. Your two risky-asset portfolio has 30% of its value in XYZ shares and the rest in shares of ABC. The volatility of XYZ and ABC are 35% and 30%, respectively, and the correlation between XYZ and ABC is 0.3. Based on this information, what is the standard deviation of your portfolio?

3. HTL Energy Shares Company had realized returns of 10%, 20%, 20%, and 10% over four quarters. What is the quarterly standard deviation of returns for the company's common stock calculated from this sample?