You have the following historical annual total returns on Terlingua Oil & Gas Exploration:

Year Annual total return (%)

2001 10%

2002 -3%

2003 8%

2004 7%

2005 13%

2006 8%

2007 1%

2008 -5%

2009 2%

2010 1%

Calculate the sample standard deviation of annual return. Do not round at intermediate steps in your calculation. Express your answer in percent.