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Subject: Re: Nice riddle

Author: Colin Frayn

Date: 03:54:35 01/09/02

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On January 07, 2002 at 20:24:01, Hans van der Zijden wrote:

>I told a friend this riddle and she is still convinced that it doesn't matter if
>you change or not. She agrees that you have 1/3 chance getting it right the
>first guess, but after one (empty) door is opened she keeps saying there are 2
>doors left, so now you have 1/2 chance if you stick to your choice. I try to
>explain it to her in all the ways I could think of, but she is as stubborn as 3
>mules. I also played this situation 30 times with and 30 times without changing.
>She thinks I was lucky and the random die showed too many times the number 1.
>Anyone an idea how to explain this to her.

I tried to convince my dad of this and I ended up writing a program to run the
test 1 million times, and sure enough, changing the door got about 2/3 correct.
In fact, when I was writing the program, it became even more obvious that this
was the correct answer and I found that, after optimisation, I was almost
writing a program to print out "2/3".  I suggest you try the same and show your
friend (but do it properly).

Cheers,
Col



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