A stock portfolio's returns are normally distributed. It has had a mean annual return of 25% with a standard deviation of 40%. The probability of a return between -41% and 91% is closest to: A. 65%. B. 95%. C. 90%.
A 90% confidence level includes the range between plus and minus 1.65 standard deviations from the mean. (91 − 25) / 40 = 1.65 and (-41 − 25) / 40 = -1.65.
