Suppose that stock Y has an expected return of 8% and the standard deviation of the return is 20%. Stock X has an expected return of 8%, a standard deviation of 10%. If the returns on the two stocks have zero correlation, and the risk-free rate is 2%, is there an arbitrage opportunity here? If so, how would you exploit it? Is it rational to hold stock A even if it has the same expected return but higher variability than stock B?