RE: Today's evil Bayesian math problem

From: Emlyn O'regan (oregan.emlyn@healthsolve.com.au)
Date: Thu Sep 11 2003 - 01:38:54 MDT

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    I think it's 4/9, but I brute forced it.

    Emlyn

    > -----Original Message-----
    > From: Eliezer S. Yudkowsky [mailto:sentience@pobox.com]
    > Sent: Thursday, 11 September 2003 3:46 PM
    > To: extropians@extropy.org
    > Subject: Re: Today's evil Bayesian math problem
    >
    >
    > Eliezer S. Yudkowsky wrote:
    > > Suppose that a bowl has 5 red chips and 3 white chips. We
    > sample chips
    > > from the bowl using the following procedure: On each round
    > we draw a
    > > random chip, replace it, and then add another chip of the
    > same color to
    > > the bowl. For example, if on the first round we happen to
    > draw a red
    > > chip, there would then be 6 red chips and 3 white chips to
    > draw from on
    > > the second round.
    > >
    > > Given that a white chip was drawn on the fourth round, what is the
    > > probability that a white chip was drawn on the second round?
    > >
    > > (This problem is extra bonus evil because it's so easy if
    > you know the
    > > rules.)
    >
    > Evil Hint #1: Not only is it possible for you to do this
    > problem in your
    > head, the answer can be obtained in ONE step.
    >
    > --
    > Eliezer S. Yudkowsky http://singinst.org/
    > Research Fellow, Singularity Institute for Artificial Intelligence
    >



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