This document discusses risk and return in investments. It defines return as the profits earned from an investment through dividends and capital appreciation. It then discusses different ways to calculate returns for single and multi-period investments. It also distinguishes between ex-post returns that have already occurred and ex-ante expected returns. The document goes on to define risk as the deviation from expected returns and discusses how standard deviation and variance are commonly used to measure risk. It also covers the benefits of diversification and how portfolio risk can be reduced through diversifying investments.