开发者:上海品职教育科技有限公司 隐私政策详情

应用版本:4.2.11(IOS)|3.2.5(安卓)APP下载

阿婉 · 2018年12月06日

问一道题:NO.PZ2017092702000073

问题如下图:

    

选项:

A.

B.

C.

解释:


  老师,请问下这个用的是哪个公式,已经把E(s)求出来了,然后用COV(S,S)=△s^2 然后我用的是 [70-E(s)]*0.05+[40-E(s)]*0.7+[25-E(s)]*0.25,结果最后de得0了。。┓( ´∀` )┏求问

2 个答案

阿婉 · 2018年12月07日

不好意思老师。。。问题有点弱智,但是还是问下……这个用的不是组合的方差公式吧。。组合的方差公式我套用不进去。。

菲菲_品职助教 · 2018年12月07日

这个不是组合的方差公式哦,因为没有涉及到两个资产,只是某公司自己的销售的概率分布而已。

菲菲_品职助教 · 2018年12月07日

同学你好,解析是直接用方差的公式的。只是乘以了各自的权重。

当然你的做法也是可以的,但是每一项都漏了平方哦,所以导致计算不正确。

应该是[70-E(s)]^2*0.05+[40-E(s)]^2*0.7+[25-E(s)]^2*0.25才对。

 

絮飛W涙 · 2018年12月08日

为什么有平方?不理解了

菲菲_品职助教 · 2018年12月08日

因为这题要先计算方差,所以是有平方的。得出方差后再开根号就是标准差。

阿婉 · 2018年12月08日

我是用COV(X,X)=△X^2,所以应该是要有平方的……但其实按照老师的说法,就是按照方差本身的性质来求(即,方差本身就是距离平方的加权平均),更简便……

菲菲_品职助教 · 2018年12月08日

对是的,其实这道题的解析就是按照方差的那个公式来求的,当然你用协方差来求其实本质也是一样的~~

  • 2

    回答
  • 1

    关注
  • 520

    浏览
相关问题

NO.PZ2017092702000073 问题如下 The probability stribution for a company’s sales is:The stanrviation of sales is closest to: A.$9.81 million. B.$12.20 million. C.$32.40 million. A is correct. The analyst must first calculate expectesales 0.05 × $70 + 0.70 × $40 + 0.25 × $25 = $3.50 million + $28.00 million + $6.25 million = $37.75 million. After calculating expectesales, we ccalculate the varianof sales: = σ2 (Sales) = P($70)[$70 – E(Sales)]2 + P($40)[$40 – E(Sales)]2 + P($25)[$25 – E(Sales)]2 = 0.05($70 – 37.75)2 + 0.70($40 – 37.75)2 + 0.25($25 – 37.75)2 = $52.00 million + $3.54 million + $40.64 million = $96.18 million. The stanrviation of sales is thus σ = ($96.18)1/2 = $9.81 million. 1

2024-04-07 16:29 1 · 回答

NO.PZ2017092702000073 问题如下 The probability stribution for a company’s sales is:The stanrviation of sales is closest to: A.$9.81 million. B.$12.20 million. C.$32.40 million. A is correct. The analyst must first calculate expectesales 0.05 × $70 + 0.70 × $40 + 0.25 × $25 = $3.50 million + $28.00 million + $6.25 million = $37.75 million. After calculating expectesales, we ccalculate the varianof sales: = σ2 (Sales) = P($70)[$70 – E(Sales)]2 + P($40)[$40 – E(Sales)]2 + P($25)[$25 – E(Sales)]2 = 0.05($70 – 37.75)2 + 0.70($40 – 37.75)2 + 0.25($25 – 37.75)2 = $52.00 million + $3.54 million + $40.64 million = $96.18 million. The stanrviation of sales is thus σ = ($96.18)1/2 = $9.81 million. 请问这道题目可以用金融计算器算吗

2023-10-22 22:47 1 · 回答

NO.PZ2017092702000073问题如下The probability stribution for a company’s sales is:The stanrviation of sales is closest to:A.$9.81 million. B.$12.20 million. C.$32.40 million. A is correct. The analyst must first calculate expectesales 0.05 × $70 + 0.70 × $40 + 0.25 × $25 = $3.50 million + $28.00 million + $6.25 million = $37.75 million. After calculating expectesales, we ccalculate the varianof sales: = σ2 (Sales) = P($70)[$70 – E(Sales)]2 + P($40)[$40 – E(Sales)]2 + P($25)[$25 – E(Sales)]2 = 0.05($70 – 37.75)2 + 0.70($40 – 37.75)2 + 0.25($25 – 37.75)2 = $52.00 million + $3.54 million + $40.64 million = $96.18 million. The stanrviation of sales is thus σ = ($96.18)1/2 = $9.81 million. 1.可不可以再一下为啥求均值就是求期望?2.这里的variance为啥不除以总个数?谢谢

2023-06-18 17:51 1 · 回答

NO.PZ2017092702000073 问题如下 The probability stribution for a company’s sales is:The stanrviation of sales is closest to: A.$9.81 million. B.$12.20 million. C.$32.40 million. A is correct. The analyst must first calculate expectesales 0.05 × $70 + 0.70 × $40 + 0.25 × $25 = $3.50 million + $28.00 million + $6.25 million = $37.75 million. After calculating expectesales, we ccalculate the varianof sales: = σ2 (Sales) = P($70)[$70 – E(Sales)]2 + P($40)[$40 – E(Sales)]2 + P($25)[$25 – E(Sales)]2 = 0.05($70 – 37.75)2 + 0.70($40 – 37.75)2 + 0.25($25 – 37.75)2 = $52.00 million + $3.54 million + $40.64 million = $96.18 million. The stanrviation of sales is thus σ = ($96.18)1/2 = $9.81 million. 答案解析第二步不明白

2023-05-26 00:04 1 · 回答

NO.PZ2017092702000073 问题如下 The probability stribution for a company’s sales is:The stanrviation of sales is closest to: A.$9.81 million. B.$12.20 million. C.$32.40 million. A is correct. The analyst must first calculate expectesales 0.05 × $70 + 0.70 × $40 + 0.25 × $25 = $3.50 million + $28.00 million + $6.25 million = $37.75 million. After calculating expectesales, we ccalculate the varianof sales: = σ2 (Sales) = P($70)[$70 – E(Sales)]2 + P($40)[$40 – E(Sales)]2 + P($25)[$25 – E(Sales)]2 = 0.05($70 – 37.75)2 + 0.70($40 – 37.75)2 + 0.25($25 – 37.75)2 = $52.00 million + $3.54 million + $40.64 million = $96.18 million. The stanrviation of sales is thus σ = ($96.18)1/2 = $9.81 million. 麻烦帮忙一下,谢谢

2022-10-02 19:09 1 · 回答