a是什么，能举个例吗

Module 4-官网习题-第51题-(1)为什么要standardize a normal random variable?什么情况下，需要标准化一个正态随机变量？(2)另外，答案中所写的：Thus, ($480,000 − $355,000)/3.0 = $41,667.Alternatively, use Z = −3, X = $230,000, and μ = $355,000: ($230,000 − $355,000)/(−3.0) = $41,667.为什么480,000用z=3,而-480,000用z=-3?(3)另外，为什么，在正态分布下, mean=(maximum+minimum)/2?这个公式在教材第几页上有写？

SEE为什么不用表格里面的standarderror的数据

Module 4-官网习题-第52题-答案中所写的：The portfolio with the highest safety-first ratio minimizes the probability that the investor’s portfolio will have a value lower than $700,000 at year end.但是教材P264所写的是，Roy’s safety-first criterion (Roy 1952) states that the optimal portfolio minimizes the probability that portfolio return, RP, will fall below the threshold level, RL. 这道题中的$700,000是threshold level RL? 另外，教材P264-Example 7上方最后一段的最后一句话，所写的：When we evaluate portfolios using the Sharpe ratio, the portfolio with the highest Sharpe ratio is the one that minimizes the probability that portfolio return will be less than the risk-free rate (given a normality assumption).这道题中的$700,000是the risk free rate(given a normality assumption)? 请问最优的Roy's Safety-First Ratio 将使什么的概率（低于什么的值）最小化？

如果题目不是等权重，答案一样吗？

如何判断z表给的是单尾还是双尾？

Module 4-官网习题-第53题-不太能理解，0.6的6次方以及0.4的4次方，应该怎么理解？在这道题里，n=10,x=6,p=0.6,请结合这道题目，分别解释下这3个变量？

题目给的10%COC是迷惑题干？

Module 4-官网习题55-B答案所说的The probability of generating a random number equal to any fixed point under a continuous uniform distribution is zero. 请问这个知识点在教材第几页上有明确说到？

Module 4-官网习题-B选项的答案解释，为什么the expected value=mean?为什么期望值等于均值？教材第几页上有讲到过这个知识点？