Message-Id: <l03110725b34c171facc8@[192.174.2.173]>
Date: Tue, 27 Apr 1999 17:44:30 -0800
To: pinhole@exploratorium.edu
From: Paul Doherty <pauld@exploratorium.edu>
Subject: probability
OK time to get hands-on here:
get a bunch of pairs of coins, siblings if you will.
Have a partner flip all the pairs.
Now have that partner select out all of the pairs that have at least one
head showing. (Hint the head is a sister)
(This means that 1/4 or so of the pairs that have 2 tails have been discarded.)
Have your assistant line up all the pairs with the coin with a head showing
and the other coin hidden.
Now ask the question: In these pairs of sibling coins one was a sister,
what was the probability that the other was a brother?
Uncover the hidden coins.
2/3 of the hidden coins are tails!
Of course you say, you threw out 1/4 of the cases.
Yes I did because that is what the problem told me to do:
In a pair of siblings one of them is the sister, therefore throw out all
the two brother pairs.
Hands-on rules!
Paul D
Paul "But it is more complicated than that!" Doherty,
Senior Staff Scientist, The Exploratorium.
pauld@exploratorium.edu, www.exo.net/~pauld