Re: help! a probablilty problem about flipping coins...
From: Keith A. Lewis (lewis_at_PROBE.MITRE.ORG)
Date: 11/17/04
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Date: Wed, 17 Nov 2004 20:09:58 +0000 (UTC)
"lucy" <losemind@yahoo.com> writes in article <cng4a3$6ej$1@news.Stanford.EDU> dated Wed, 17 Nov 2004 10:12:18 -0800:
>Suppose we flip a unfair coin with prob. p it is head, with prob. 1-p it is
>tail.
>
>So the prob. of head is p, a prior probablity.
>
>I flip the coin N times,
>
>what is the a posterprior prob. of head if I know that there are at least K
>heads? i.e. given at least K heads?
>
>what is the prob. of getting M heads out of these N flippings given at least
>K heads occurred?
The probability of exactly M heads is given by the binomial distribution.
P(M) = p^M * (1-p)^(N-M) * choose(N,M)
The probability of event A given event B is:
P(A|B) = P(A&B) / P(B)
[The | character means "given" in this context; & means "and"]
That should get you started.
--Keith Lewis klewis {at} mitre.org
The above may not (yet) represent the opinions of my employer.
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