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February 14th, 2016, 08:41 AM  #1 
Newbie Joined: Feb 2016 From: Canada Posts: 4 Thanks: 0  Math : discrete probability distribution
We ask a person to taste 18 biscuits , 8 made to butter ( the other 10 are made to margarine ) , and to identify 8 butter cookies . He does not know the exact number of butter cookies . As he sees no difference , he randomly selects those he claims to be butter . Y = the number of butter cookies correctly identified. Indicate , the variance of the variable Y. the number of "butter" guesses is binomial with parameters n = 18 and p = 0.5. If X of his guesses are "butter", some of these may be truly butter cookies and some not; the number of "butter" guesses that are truly "butter" is Y. Can someone please help me I have been trying to do this problem for 4 hours 
February 14th, 2016, 05:46 PM  #2 
Senior Member Joined: Dec 2012 From: Hong Kong Posts: 853 Thanks: 311 Math Focus: Stochastic processes, statistical inference, data mining, computational linguistics 
I think Y~Binomial(n = 8, p=0.5). Whether he correctly identifies a margarine cookie as margarine or misidentifies it as butter doesn't affect Y.

February 14th, 2016, 06:36 PM  #3 
Newbie Joined: Feb 2016 From: Canada Posts: 4 Thanks: 0  
February 15th, 2016, 06:42 AM  #4 
Senior Member Joined: Dec 2012 From: Hong Kong Posts: 853 Thanks: 311 Math Focus: Stochastic processes, statistical inference, data mining, computational linguistics 
Can I know the numerical answer? 
February 15th, 2016, 01:52 PM  #5 
Global Moderator Joined: May 2007 Posts: 6,807 Thanks: 717  

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discrete, distribution, math, probability 
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