andrew plans to retire in 40 years. he plans to invest part of his retirement funds in stocks, so he seeks out information on past returns. he learns that over the entire 20th century, the real (that is, adjusted for inflation) annual returns to U.S. common stocks had mean 8.7% and standard deviation of 20.2% . the distribution of annual returns on common stocks is roughly symmetric, so the mean return over even a moderate of years is close to normal. what is the probability (assuming that the past patterns of variation continues) that the mean annual return on common stock over the next 40 years will
a. exceed 10% ?
b. be less than 5%?

Question

andrew plans to retire in 40 years. he plans to invest part of his retirement funds in stocks, so he seeks out information on past returns. he learns that over the entire 20th century, the real (that is, adjusted for inflation) annual returns to U.S. common stocks had mean 8.7% and standard deviation of 20.2% . the distribution of annual returns on common stocks is roughly symmetric, so the mean return over even a moderate of years is close to normal. what is the probability (assuming that the past patterns of variation continues) that the mean annual return on common stock over  the next 40  years will 
a. exceed 10% ?
b. be less than 5%?