NO.PZ2018062016000088
问题如下：
A stock obeying normal distribution has a mean return of 6% and a standard deviation of 18%. The probability for the stock's return to fall less than 4% is:
N(0.11) = 0.5438
选项：
A. 37.91%
B. 45.62%
C. 57.68%
解释：
B is correct. Firstly, standardize the original normal distribution：Z= (x-6%)/18%, so P(x <4%) = P( Z<-0.11).
Notice that N(-0.11) = 1- N(0.11). Based on the given condition, N(0.11) = 0.5438, so N(-0.11) = 1-0.5438 = 0.4562 = 45.62%
这道题哪句话说的是Z分布，另外x为什么是4呢？不太明白这道题目的意思
