Q) In Joe’s café 70% of customers buy a cup of tea.
In a random sample of 20 customers find the probability that more than 15 buy a cup of tea.
A) Let X the number out of 20 who buy a cup of tea.
X ~ B(20, 0.7)
Since 0.7 is not in the tables, you will need to consider the, complementary random variable Y.
Let Y the number of customers who do not buy a cup of tea.
Y ~ B(20, 0.3)
P(X>15) = P(Y≤4) = 0.2375
我的疑問來了, 0.2375不是the probability that " number of customers who do not buy a cup of tea"嗎???但問題是"find the probability that more than 15 buy a cup of tea".....我真的搞唔明白~
有關Binomial distribution的問題
2013-03-10 9:50 am
回答 (2)
2013-03-13 5:51 am
✔ 最佳答案
X 是買咖啡的人數﹐Y是不買咖啡的人數因為樣本大小是20﹐超過15人買咖啡等同於少於5人不買咖啡
因此P(X>15) = P(Y≤4) = 0.2375
希望幫到你
2013-03-10 11:46 pm
p=0.7, q=1-p=0.3c(20,x)=20!/[x!(20-x)!](1) f(x)=c(20,x)*p^x*q^(20-x)P(x>15)=f(16)+f(17)+f(18)+f(19)+f(20)=c(20,16)*p^16*q^4+c(20,17)*p^17*q^3+c(20,18)*p^18*q^2+c(20,19)*p^19*q+c(20,20)*p^20=0.2375(2) g(x)=c(20,x)*q^x*p^(20-x)P(x<5)=f(0)+f(1)+f(2)+f(3)+f(4)=0.2375f(x).g(x)擁有相同的意義!!
收錄日期: 2021-04-27 17:45:15
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20130310000051KK00034