The historical stock returns for GAF, Inc. are listed below:

Year Annual Stock Return

2005 12%

2006 18%

2007 38%

2008 -12%

2009 0%

2010 -18%

2011 15%

2012 27%

What is the standard deviation of returns for GAF, Inc. stock over the 8 year time period? (Compute the standard deviation assuming this is a population of returns, not a sample - that is, use the procedure described in the textbook for calculating the standard deviation of a series of stock returns).