An investment in the S&P 500 has an expected return of 8.7 percent per year with a standard deviation of 14 percent (this is down from the 18% observed in decades past). Assuming that the returns on this investment are at least roughly normally distributed, how frequently do you expect to earn between -5.3 percent and +22.7 percent? How often do you expect to earn less than -5.3 percent?