Andrew plans to retire in 40 years. He plans to invest part of his retirement funds in stocks, so he seeks out info on past returns. Over the 20th century the real annual return on U.S common stocks had mean 8.7% and standard deviation 20.2%. The distribution of annual returns on common stocks is roughly symmetrical, so the mean return over an even moderate number of years is close to normal. What is the probability that the mean return will be less then 5%?