Assume that we know the performance of the S&P 500 Index for the first five years of the second decade of the 21st century, defined as 2010–2019. What annual geometric mean must the market average for the last five years (2015–2019) to produce an over- all geometric mean for the decade of 10 percent? The returns for the first five years are 2010, 15.06 percent; 2011, 9.9 percent; 2012, 16.1 percent; 2013, 19.7 percent; and 2014, 10.7 percent.