Returns for the Shields Company over the last three years are shown below. Whats the standard deviation of Shields returns? ( Hint: This is a sample, not a complete population, so the sample standard deviation formula should be used.)

Year	Return
2009	21.50%
2008	12.50%
2007	24.20%

a.

20.97%

b.

21.49%

c.

19.94%

d.

20.46%

How would this be solved WITHOUT EXCEL in the most simple way? Thanks