You are considering an investment in either individual stocks or a portfolio of stocks. The two stocks you are researching, stocks A and B, have the following historical returns:

Year RA RB

2009 20% 5%

2010 42% 15%

2011 20% 13%

2012 8% 50%

2013 25% 12%

Calculate the standard deviation of returns for each stock and for the portfolio.

I know the answersto be

A-25.3

B 24.3

portfilio 16.3

However, I am not able to figure out how to get ther.

I need step by step please.