作者rock1985 (疾风)
看板Math
标题[机统] 机率统计问题
时间Sat Apr 23 12:54:46 2011
The monthly revenue for a Wal-Mart store is normally distributed with the
average equal to $8.2 million and the standard deviation equal to $1.3 million
1)What is the probability that a randomly selected Wal-Mart store has
monthly revenue exceeding $10 million.
2)What is the threshold value that defines the highest 10 percent of monthly
revenue at a Wal-Mart store.
3)A sample of 34 Wal-Mart store is randomly selected, what is the probability
that the average monthly revenue of the sample exceeds $8 million.
题目是我朋友的mid-term 虽然我学过一点机率统计
但是实在不知道要怎麽解题
只知道可能会用到Z-chart之类的来解题
所以想请问大家一下要怎麽解题
可以稍微帮我朋友 顺便帮我复习一下
感谢大家
第2题的部分
我想到的是从平均值去加一个某个大小的标准差
去计算10%的位置在哪里
不过还是不太确定，所以麻烦大家教我一下
Thank you
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1F：推 vicwk :Q(1.281552) = 0.1 04/23 13:21
2F：→ yhliu :X～N(8.2,1.3^2), P[X>10]=1-Φ((10-8.2)/1.3) 04/23 13:51
3F：→ yhliu :3) Xbar～N(8.2,1.3^2/34) 04/23 13:52
4F：→ yhliu :P[Xbar>8] = 1-Φ((8-8.2)/(1.3/√34)) 04/23 13:53