The document discusses probability-based approaches for calculating expected returns and variance under uncertainty. It provides an example using return data for a stock to calculate the expected return of 9.25% and variance of 0.02%. It also discusses how portfolio return and variance depends on asset weights, the individual asset expected returns and variances, and the correlation between the assets. Assuming the two example assets are perfectly negatively correlated, it calculates the asset weights needed for a zero risk portfolio and the expected return of that portfolio as 25.36%. Finally, it discusses limits to diversification in practice, such as the inability to hold all securities and that only unsystematic risk can be reduced through diversification.