The expected rate of return on the market is 12% and risk-free rate is 7%. The standard deviation on the return on market is 15%. One investor creates a portfolio on efficient frontier with an expected return of 10%. Another makes a portfolio on the efficient frontier with expected frontier with an expected rate of return of 20%. Determine the standard deviation of the returns of the two portfolios?
Please show work as the textbook does not explain much nor give an example.