The average annual return for the S\&P 500 from 1886 to 2006 is 9.5%, with a standard deviation of 18%. Based on these numbers, what is a 95% confidence interval for 2007's returns? The average annual return for the S\&P 500 from 1886 to 2006 is 15%, with a standard deviation of 25%. Based on these numbers, what is a 95\% confidence interval for 2007's returns