Over the last 12 months an investment in the Vanguard Total Market Index returned 23.4 percent with a standard deviation of 33.4 percent (far more than the typical 8% return and with more risk than the historical 18% standard deviation). Assuming that the returns on this investment are normally distributed, how frequently do you expect to earn between -10.0 percent and 56.8 percent? How often do you expect to earn less than -10.0 percent?