Answer:
a: 12.8%
Explanation:
Standard Deviation would be calculated with the probability approach since there is probability given in the question.
Calculating ERR:
ERR= Sum of Probabilities × Rate of returns.
In our question = ERR= 0.2 × 30% + 0.5 × 10% + 0.3 × (-6%) = 0.128 = 12.8%
Thus, by putting all the values in the formula you will get the answer 12.8%.