Answer: 12.91%
Step-by-step explanation:
The mean is;
= (5% + 15% - 15% - 5%)/4
= 0
Standard deviation = √((∑(Return-mean)^2)/[time period-1])
= (√((5-0)^2 + (15-0)^2 + (-15-0)^2 + (-5-0)^2)/ (4 -1))
= √((25% + 225% + 225% + 25% ) / 3 )
= √(500/3)
= 12.91%
NB - Options are for a different question.