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DAWS · 2023年01月31日

请问这道题 3-5是要标准化先吗?

NO.PZ2020010303000009

问题如下:

Either using a Z table or the Excel function NORM.S.DIST, compute

a. Pr(-1.5 < Z < 0), where Z ∼ N(0, 1)

b. Pr(Z < -1.5), where Z ∼ N(0, 1)

c. Pr(-1.5 < X < 0), where X ∼ N(1, 2)

d. Pr(X > 2), where X ∼ N(1, 2)

e. Pr(W > 12), where W ∼ N(3, 9)

选项:

解释:

a. 43.3%. In Excel, the command to compute this value is NORM.S.DIST(0,TRUE) – NORM.S.DIST(-1.5,TRUE).

b. 6.7%. In Excel, the command to compute this value is NORM.S.DIST(-1.5,TRUE).

c. 20.1%. In Excel, the command to compute this value is NORM.S.DIST((0 – 1)/SQRT(2),TRUE) – NORM.S.DIST((-1.5-1)/SQRT(2),TRUE).

d. 24.0%. In Excel, the command to compute this value is 1 – NORM.S.DIST((2 – 1)/SQRT(2),TRUE).

e. 0.13%. In Excel, the command to compute this value is 1 – NORM.S.DIST((12 – 3)/3,TRUE).

具体怎么做呢?请问能用算式解释一下吗

2 个答案

pzqa27 · 2023年02月01日

嗨,爱思考的PZer你好:


你算的没错,答案是基于excel算的,算的比较精确,小数点保留的比较多而已

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虽然现在很辛苦,但努力过的感觉真的很好,加油!

pzqa27 · 2023年01月31日

嗨,从没放弃的小努力你好:


3-5确实是要标准化,对于正态分布的标准化直接带公式计算可以。我就用d问为例展开下,剩下的同学自己举一反三吧,原理都是一样的

比如d问的是X>2的概率,而X服从均值为1,方差为2的正态分布。 已知方差为2,那么标准差是根号2,大概是1.414左右,然后把X=2转化到01的标准正态分布中,计算:

(2-1)/1.414=1/1.414=0707213579,然后查表找到0.07213579对应的累积概率,大概是76%,那么累积概率代表的X<2的概率,我们要找到X>2的概率,用1-76%=24%

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虽然现在很辛苦,但努力过的感觉真的很好,加油!

DAWS · 2023年02月01日

谢谢老师,比如这个C问,我算出来是:-0.7071 和 -1.76, 查表得出概率是0.2206 - 0.093 大概等于18%,但是题目答案是20.1%,我是哪里算错了吗

DAWS · 2023年02月01日

查表得出是0.2206 - 0.0384, 前面那条打错了。

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