Message-Id: <l03110717b3480f5655b4@[192.174.2.173]>
Date: Sat, 24 Apr 1999 16:17:17 -0800
To: pinhole@exploratorium.edu
From: Paul Doherty <pauld@exploratorium.edu>
Subject: Re: pinhole probability
Ian, If parents have two children, there are four time- ordered possibilities:
>
>1) girl girl
>2) girl boy
>3) boy girl
>4) boy boy
>
>Assuming that
>A) these are equally likely ( Prob = 1/4 each)
>and
>B) If you meet a girl it is equally likely that she is in category 1) 2) or 3)
>
>then the odds brother:sister = 2:1
>
>
>If you meet a girl who is first born, the answer is 1:1
>The surprise comes because the 4 categories are labelled by both sex (2
>possibilities) and order of birth (2 possibilities). 2x2 = 4 categories
>
>This is a good problem because its solution utilizes the general approach
>of enumerating all possibilities and then seeing which of them satisfy the
>criteria or conditions of the posed question. The Monte Hall problem works
>the same way.
>
>... Thomas
>
>
>
>
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld