Proability Rate of Return (Quants) return, standard, following, developed

hardwork24

An analyst developed the following probability distribution of the rate of return for a common stock
Scenario Probability Rate of Return
1 0.25 0.08
2 0.50 0.12
3 0.25 0.16
The standard deviation of the rate of return is closest to
A. 0.0200
B. 0.0267
C. 0.0283
D. 0.0400

Answer:C
Expected value=0.12
Variance=0.0008
Standard deviation=0.028

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Anyone know why the ans is C.