NO.PZ2020021205000060
问题如下:
A stock has an expected return of 15% and a volatility of 20%. The current price of the stock is USD 50. Estimate a 99% confidence interval for the price at the end of one day.
选项:
解释:
Here, we are dealing with a short time period, and so it is reasonable to assume that the return is normally distributed. The return has a mean of 15% X (1 /252) = 0.0595%, and a standard deviation of 20% X = 1.2599%. The 99% confidence interval for the percentage return is between:
0.0595 - 1.2599 X (0.995) = -3.186%
and
0.0595 + 1.2599 X (0.995)= +3.305%
The confidence interval for the stock price is therefore between 50 X 0.96814 = 48.4 and
50 X 1.03305 = 51.7.
我算出来的 99% confidence interval for the percentage return is between:
- 0.0595%+2.33*1.2599%=2.995%
- 0.0595%-2.33*1.2599%=-2.876%
为什么跟解析不一样?