问题如下:
A fund manager finds that the return of funds in the market are normally distributed having a mean of $170,000 and a standard deviation of $25,000. The percent of stock incomes greater than $245,000 is closest to:
选项:
A. 0.50%.
B. 2.28%.
C. 0.13%.
解释:
C is correct.
Z=(245000 - 170000)/25000=F(3)
1 - F(3) = 1 - 0.9987 = 0.0013.
为什么1.65,1.96,2.58这些数可以用作是Z带入算题目呢?这些数不是代表落在这些数的倍数的标准差内吗?