Drawing/sampling with replacement (Probability/Combinatorics)












0












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We have an urn with $w$ white marbles and $b$ black marbles and we draw $n$ marbles with replacement. We want to know the probability of drawing $k$ white marbles ($k<n$) and apparently we use the following formula:



$$frac{binom{n}{k}w^kb^{n - k}}{(w + b)^n}$$



What is the logic/intuition behind it?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
    $endgroup$
    – herb steinberg
    Dec 3 '18 at 17:47
















0












$begingroup$


We have an urn with $w$ white marbles and $b$ black marbles and we draw $n$ marbles with replacement. We want to know the probability of drawing $k$ white marbles ($k<n$) and apparently we use the following formula:



$$frac{binom{n}{k}w^kb^{n - k}}{(w + b)^n}$$



What is the logic/intuition behind it?










share|cite|improve this question











$endgroup$








  • 1




    $begingroup$
    The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
    $endgroup$
    – herb steinberg
    Dec 3 '18 at 17:47














0












0








0





$begingroup$


We have an urn with $w$ white marbles and $b$ black marbles and we draw $n$ marbles with replacement. We want to know the probability of drawing $k$ white marbles ($k<n$) and apparently we use the following formula:



$$frac{binom{n}{k}w^kb^{n - k}}{(w + b)^n}$$



What is the logic/intuition behind it?










share|cite|improve this question











$endgroup$




We have an urn with $w$ white marbles and $b$ black marbles and we draw $n$ marbles with replacement. We want to know the probability of drawing $k$ white marbles ($k<n$) and apparently we use the following formula:



$$frac{binom{n}{k}w^kb^{n - k}}{(w + b)^n}$$



What is the logic/intuition behind it?







probability combinatorics






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 4 '18 at 11:11









N. F. Taussig

44.4k93357




44.4k93357










asked Dec 3 '18 at 17:43









E.KE.K

6




6








  • 1




    $begingroup$
    The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
    $endgroup$
    – herb steinberg
    Dec 3 '18 at 17:47














  • 1




    $begingroup$
    The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
    $endgroup$
    – herb steinberg
    Dec 3 '18 at 17:47








1




1




$begingroup$
The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
$endgroup$
– herb steinberg
Dec 3 '18 at 17:47




$begingroup$
The formula is essentially that of the binomial distribution. en.wikipedia.org/wiki/Binomial_distribution
$endgroup$
– herb steinberg
Dec 3 '18 at 17:47










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