[dba-Tech] The Three Doors Problem

But if I pick Door B and Door B is still closed when I am offered my choice 
and don't change and Door B is opened and contains nothing then I lose.

If I do change an choose door A then I win

However if I change to Door A and Door B contains the prize then I lose.

When I make the decision to change door I have a 50/50 chance of winning. I 
am left with two doors. Forget door 3 it doesn't exist any more as an 
option.

Martin


----- Original Message ----- 
From: "Stuart McLachlan" <stuart at lexacorp.com.pg>
To: "Discussion of Hardware and Software issues" 
<dba-tech at databaseadvisors.com>
Sent: Friday, August 26, 2005 1:01 PM
Subject: Re: [dba-Tech] The Three Doors Problem


> On 26 Aug 2005 at 13:40, Lembit Soobik wrote:
>
>> I think you make it too complicated.
>> forget the history.
>
> That's the flaw in your argument. You can't forget the history.
>
>> at the end, what you have is two doors:
>> one is the winning door
>> just pick one.
>> doesnt matter what you had picked before
>
> Yes it does.
>
>> doesnt matter whether you swap or not.
>
> Yes it does.
>
>> and you can write simulation programs till the cows come home
>
> And if they are written correctly, they will give you the correct answer
> over enough trials.
>
>> fact is you have one right and one wrong and have to pick one
>> so you have 1 out of two chance thats all.
>>
>
> Fact is, when you first picked you had three choices.
>
> The odds are 1/3 you are right initially.  In that one case, switching is
> wrong.
>
> In the 2/3 where you were wrong initially, changing will always give you
> the correct door. (Assuming the problem is stated correctly. As I said
> previous, you need to qualify it by saying "I open another door
> which I know contains a dead fish and show you the contents"  If you could
> open the money door by accident, it is a different situation.)
>
> So in 1/3 cases you win by staying, in 2/3 cases you win by switching.
>
> -- 
> Stuart
>
>
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