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February 14th, 2016, 08:41 AM   #1
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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
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February 14th, 2016, 05:46 PM   #2
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I think Y~Binomial(n = 8, p=0.5). Whether he correctly identifies a margarine cookie as margarine or mis-identifies it as butter doesn't affect Y.
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February 14th, 2016, 06:36 PM   #3
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Quote:
Originally Posted by 123qwerty View Post
I think Y~Binomial(n = 8, p=0.5). Whether he correctly identifies a margarine cookie as margarine or mis-identifies it as butter doesn't affect Y.
So I just do
Variance= n*p*q
8*0.5*0.5 ?
That doesnt give me the right answer
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February 15th, 2016, 06:42 AM   #4
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Can I know the numerical answer?
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February 15th, 2016, 01:52 PM   #5
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Quote:
Originally Posted by 123qwerty View Post
I think Y~Binomial(n = 8, p=0.5). Whether he correctly identifies a margarine cookie as margarine or mis-identifies it as butter doesn't affect Y.
p=4/9
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