標題:
有關Binomial distribution的問題
發問:
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... 顯示更多 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~
最佳解答:
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
其他解答:
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
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