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Re: Toughest Game Show Question

Started byBill Reid <hormelfree@gmail.com>
First post2012-01-10 06:47 -0800
Last post2012-01-14 23:38 -0500
Articles 20 on this page of 38 — 21 participants

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  Re: Toughest Game Show Question Bill Reid <hormelfree@gmail.com> - 2012-01-10 06:47 -0800
    Re: Toughest Game Show Question tom st denis <tom@iahu.ca> - 2012-01-10 07:11 -0800
      Re: Toughest Game Show Question falk@rahul.net (Edward A. Falk) - 2012-01-11 00:05 +0000
    Re: Toughest Game Show Question Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-01-10 11:23 -0500
    Re: Toughest Game Show Question John Gordon <gordon@panix.com> - 2012-01-10 16:48 +0000
      Re: Toughest Game Show Question Seebs <usenet-nospam@seebs.net> - 2012-01-10 19:15 +0000
        Re: Toughest Game Show Question Keith Thompson <kst-u@mib.org> - 2012-01-10 13:27 -0800
          Re: Toughest Game Show Question James Kuyper <jameskuyper@verizon.net> - 2012-01-10 16:57 -0500
          Re: Toughest Game Show Question Seebs <usenet-nospam@seebs.net> - 2012-01-10 22:39 +0000
    Re: Toughest Game Show Question Stephen Sprunk <stephen@sprunk.org> - 2012-01-10 11:21 -0600
      Re: Toughest Game Show Question Bill Reid <hormelfree@gmail.com> - 2012-01-10 15:43 -0800
        Re: Toughest Game Show Question Stephen Sprunk <stephen@sprunk.org> - 2012-01-10 22:53 -0600
          Re: Toughest Game Show Question Seebs <usenet-nospam@seebs.net> - 2012-01-11 05:00 +0000
            Re: Toughest Game Show Question Kaz Kylheku <kaz@kylheku.com> - 2012-01-11 06:32 +0000
            Re: Toughest Game Show Question James Kuyper <jameskuyper@verizon.net> - 2012-01-11 07:22 -0500
        Re: Toughest Game Show Question falk@rahul.net (Edward A. Falk) - 2012-01-12 22:51 +0000
          Re: Toughest Game Show Question Ian Collins <ian-news@hotmail.com> - 2012-01-13 12:14 +1300
          Re: Toughest Game Show Question ImpalerCore <jadill33@gmail.com> - 2012-01-12 15:17 -0800
    Re: Toughest Game Show Question Shao Miller <sha0.miller@gmail.com> - 2012-01-10 14:33 -0500
    Re: Toughest Game Show Question Kaz Kylheku <kaz@kylheku.com> - 2012-01-11 01:44 +0000
      Re: Toughest Game Show Question Dann Corbit <dcorbit@connx.com> - 2012-01-10 23:48 -0800
        Re: Toughest Game Show Question James Kuyper <jameskuyper@verizon.net> - 2012-01-11 07:23 -0500
      Re: Toughest Game Show Question "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2012-01-11 14:33 +0100
        Re: Toughest Game Show Question Willem <willem@toad.stack.nl> - 2012-01-11 13:48 +0000
          Re: Toughest Game Show Question "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2012-01-11 18:44 +0100
            Re: Toughest Game Show Question Willem <willem@toad.stack.nl> - 2012-01-11 18:10 +0000
              Re: Toughest Game Show Question "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2012-01-11 19:23 +0100
            Re: Toughest Game Show Question James Kuyper <jameskuyper@verizon.net> - 2012-01-12 18:23 -0500
              Re: Toughest Game Show Question "M. Strobel" <sorry_no_mail_here@nowhere.dee> - 2012-01-15 19:03 +0100
              Re: Toughest Game Show Question Willem <willem@toad.stack.nl> - 2012-01-15 19:42 +0000
                Re: Toughest Game Show Question James Kuyper <jameskuyper@verizon.net> - 2012-01-15 16:57 -0500
                Re: Toughest Game Show Question Kaz Kylheku <kaz@kylheku.com> - 2012-01-16 04:16 +0000
                  Re: Toughest Game Show Question gazelle@shell.xmission.com (Kenny McCormack) - 2012-01-16 12:14 +0000
                    Re: Toughest Game Show Question Bill Reid <hormelfree@gmail.com> - 2012-01-17 07:31 -0800
                  Re: Toughest Game Show Question Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-26 09:33 -0800
      Re: Toughest Game Show Question "BartC" <bc@freeuk.com> - 2012-01-12 21:07 +0000
        factor jgk@panix.com (Joe keane) - 2012-01-12 22:53 +0000
        Re: Toughest Game Show Question pete <pfiland@mindspring.com> - 2012-01-14 23:38 -0500

Page 1 of 2  [1] 2  Next page →


#15684 — Re: Toughest Game Show Question

FromBill Reid <hormelfree@gmail.com>
Date2012-01-10 06:47 -0800
SubjectRe: Toughest Game Show Question
Message-ID<78ecc52b-cc20-477c-9a83-dadd3b46d1ff@u20g2000yqb.googlegroups.com>
On Jan 9, 8:56 pm, divya bisht <bisht88.di...@gmail.com> wrote:
>
> You are on a game show and there are three doors. The presenter tells
> you that behind one of doors there is a car and behind the other two
> are goats, if you pick the car you win it. After you have picked a
> door the presenter opens a different door with a goat behind it, he
> then gives you the chance to change what door you open, what should
> you do?
>
OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
USENET!!!!!!!

The answer is that it doesn't matter, your odds are still one
in three no matter what you do...but wait, does it matter if the
presenter knows what's behind the doors and shows you the goat
to make the game more interesting?  Let's see what happens with
the "regs" here, might be fun...

---
William Ernest Reid

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#15685

Fromtom st denis <tom@iahu.ca>
Date2012-01-10 07:11 -0800
Message-ID<366ccd1c-1fa0-476b-af37-103815d659b0@a40g2000vbu.googlegroups.com>
In reply to#15684
On Jan 10, 9:47 am, Bill Reid <hormelf...@gmail.com> wrote:
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
>
> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do...but wait, does it matter if the
> presenter knows what's behind the doors and shows you the goat
> to make the game more interesting?  Let's see what happens with
> the "regs" here, might be fun...

Never switch your bet.  Pigeons know it.

Tom

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#15721

Fromfalk@rahul.net (Edward A. Falk)
Date2012-01-11 00:05 +0000
Message-ID<jeijoh$74u$1@blue-new.rahul.net>
In reply to#15685
In article <366ccd1c-1fa0-476b-af37-103815d659b0@a40g2000vbu.googlegroups.com>,
tom st denis  <tom@iahu.ca> wrote:
>On Jan 10, 9:47 am, Bill Reid <hormelf...@gmail.com> wrote:
>> OH NO, THE DREADED "MONTY HALL" PROBLEM ...

Ooooh, I love that problem.  I've made money on that one.

>Never switch your bet.  Pigeons know it.

That's why they're called "pigeons".

The key is that Monty knows where the goats are, and thus
introduces information into the game when he opens a door.
Thus, you should always switch.  Math on request.

-- 
	-Ed Falk, falk@despams.r.us.com
	http://thespamdiaries.blogspot.com/

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#15686

FromEric Sosman <esosman@ieee-dot-org.invalid>
Date2012-01-10 11:23 -0500
Message-ID<jehole$5o6$1@dont-email.me>
In reply to#15684
On 1/10/2012 9:47 AM, Bill Reid wrote:
> On Jan 9, 8:56 pm, divya bisht<bisht88.di...@gmail.com>  wrote:
>>
>> You are on a game show and there are three doors. The presenter tells
>> you that behind one of doors there is a car and behind the other two
>> are goats, if you pick the car you win it. After you have picked a
>> door the presenter opens a different door with a goat behind it, he
>> then gives you the chance to change what door you open, what should
>> you do?
>>
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
>
> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do...but wait, does it matter if the
> presenter knows what's behind the doors and shows you the goat
> to make the game more interesting?  Let's see what happens with
> the "regs" here, might be fun...

     Stick with the original choice. You can't eat a car.

-- 
Eric Sosman
esosman@ieee-dot-org.invalid

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#15688

FromJohn Gordon <gordon@panix.com>
Date2012-01-10 16:48 +0000
Message-ID<jehq41$qa9$1@reader1.panix.com>
In reply to#15684
In <78ecc52b-cc20-477c-9a83-dadd3b46d1ff@u20g2000yqb.googlegroups.com> Bill Reid <hormelfree@gmail.com> writes:

> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do

It does matter.  If you switch, you have a two-in-three chance of winning.

> ..but wait, does it matter if the presenter knows what's behind the
> doors and shows you the goat to make the game more interesting?

The presenter does know.  He doesn't open a random door.

-- 
John Gordon                   A is for Amy, who fell down the stairs
gordon@panix.com              B is for Basil, assaulted by bears
                                -- Edward Gorey, "The Gashlycrumb Tinies"

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#15695

FromSeebs <usenet-nospam@seebs.net>
Date2012-01-10 19:15 +0000
Message-ID<slrnjgp2v2.1hfs.usenet-nospam@guild.seebs.net>
In reply to#15688
On 2012-01-10, John Gordon <gordon@panix.com> wrote:
> The presenter does know.  He doesn't open a random door.

Our spammy friend seems to have a religious objection to an unambiguous
problem statement, and has not specified this.

-s
-- 
Copyright 2011, all wrongs reversed.  Peter Seebach / usenet-nospam@seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
I am not speaking for my employer, although they do rent some of my opinions.

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#15705

FromKeith Thompson <kst-u@mib.org>
Date2012-01-10 13:27 -0800
Message-ID<lnboqb459k.fsf@nuthaus.mib.org>
In reply to#15695
Seebs <usenet-nospam@seebs.net> writes:
> On 2012-01-10, John Gordon <gordon@panix.com> wrote:
>> The presenter does know.  He doesn't open a random door.
>
> Our spammy friend seems to have a religious objection to an unambiguous
> problem statement, and has not specified this.

The question does say that the presenter opens a door with a goat behind
it.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
    Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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#15707

FromJames Kuyper <jameskuyper@verizon.net>
Date2012-01-10 16:57 -0500
Message-ID<4F0CB44E.3070103@verizon.net>
In reply to#15705
On 01/10/2012 04:27 PM, Keith Thompson wrote:
> Seebs <usenet-nospam@seebs.net> writes:
>> On 2012-01-10, John Gordon <gordon@panix.com> wrote:
>>> The presenter does know.  He doesn't open a random door.
>>
>> Our spammy friend seems to have a religious objection to an unambiguous
>> problem statement, and has not specified this.
> 
> The question does say that the presenter opens a door with a goat behind
> it.

Yes, but it doesn't say whether he opened a random door that happened to
have a goat behind it, or whether he deliberately choose a door that he
knew had a goat behind it. The latter is, I believe, the intended
situation in the standard "Monty Hall" problem. A lot of very confusing
discussions about that problem have been based upon choosing a different
assumption. To take the most extreme case: what if the presenter only
bothers opening the second door if you happen to have already chosen the
correct door, and otherwise leaves it closed (obviously, you've not been
informed of this policy)?

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#15712

FromSeebs <usenet-nospam@seebs.net>
Date2012-01-10 22:39 +0000
Message-ID<slrnjgpf72.1ns3.usenet-nospam@guild.seebs.net>
In reply to#15705
On 2012-01-10, Keith Thompson <kst-u@mib.org> wrote:
> Seebs <usenet-nospam@seebs.net> writes:
>> On 2012-01-10, John Gordon <gordon@panix.com> wrote:
>>> The presenter does know.  He doesn't open a random door.

>> Our spammy friend seems to have a religious objection to an unambiguous
>> problem statement, and has not specified this.

> The question does say that the presenter opens a door with a goat behind
> it.

But it does not say whether we know that the presenter ALWAYS does this,
or whether it's just that, on this single case, the presenter HAPPENED to
do this.

Imagine that you were running a game show for people who are familiar with
this problem; the host strategy would be to always show people a goat if they
picked the car, and not show them a goat if they already picked one.  Then
people who know the problem in the formulation where the host *must* always
show you a goat will end up losing every time, because they only get the option
to switch when doing so will hurt them.

In the real show, the host chose whether or not to reveal another door in
a way that made it not obvious that you were better off switching, because
part of it was his read of the contestants.

-s
-- 
Copyright 2011, all wrongs reversed.  Peter Seebach / usenet-nospam@seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
I am not speaking for my employer, although they do rent some of my opinions.

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#15690

FromStephen Sprunk <stephen@sprunk.org>
Date2012-01-10 11:21 -0600
Message-ID<jehs3m$oju$1@dont-email.me>
In reply to#15684
On 10-Jan-12 08:47, Bill Reid wrote:
> On Jan 9, 8:56 pm, divya bisht <bisht88.di...@gmail.com> wrote:
>> You are on a game show and there are three doors. The presenter tells
>> you that behind one of doors there is a car and behind the other two
>> are goats, if you pick the car you win it. After you have picked a
>> door the presenter opens a different door with a goat behind it, he
>> then gives you the chance to change what door you open, what should
>> you do?
>>
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
> 
> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do...but wait, does it matter if the
> presenter knows what's behind the doors and shows you the goat
> to make the game more interesting?  Let's see what happens with
> the "regs" here, might be fun...

Mythbusters recently tested this.  You're always better off switching.

S


-- 
Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking

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#15720

FromBill Reid <hormelfree@gmail.com>
Date2012-01-10 15:43 -0800
Message-ID<5a07f9e0-4011-45cb-aec3-0c9c7f888d1e@f11g2000yql.googlegroups.com>
In reply to#15690
On Jan 10, 9:21 am, Stephen Sprunk <step...@sprunk.org> wrote:
> On 10-Jan-12 08:47, Bill Reid wrote:
> > On Jan 9, 8:56 pm, divya bisht <bisht88.di...@gmail.com> wrote:
>
> >> You are on a game show and there are three doors. The presenter tells
> >> you that behind one of doors there is a car and behind the other two
> >> are goats, if you pick the car you win it. After you have picked a
> >> door the presenter opens a different door with a goat behind it, he
> >> then gives you the chance to change what door you open, what should
> >> you do?
>
> > OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> > DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> > USENET!!!!!!!
>
> > The answer is that it doesn't matter, your odds are still one
> > in three no matter what you do...but wait, does it matter if the
> > presenter knows what's behind the doors and shows you the goat
> > to make the game more interesting?  Let's see what happens with
> > the "regs" here, might be fun...
>
> Mythbusters recently tested this.  You're always better off switching.
>
Did they use a Monte Carlo simulation where they fired cannonballs
through the garage doors of dozens of innocent people to see whether
there was a goat or car in the garage?

You're always better off switching, EXCEPT if the presenter
knows you've chosen the car and ONLY offers you a different
door to potentially keep you from winning the car.  In THAT case,
you WILL win the car 1/3 of the time overall, and will win
100% of the time when you decline the switch...so the behavior
of the presenter DOES make a difference...

---
William Ernest Reid

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#15724

FromStephen Sprunk <stephen@sprunk.org>
Date2012-01-10 22:53 -0600
Message-ID<jej4k4$166$1@dont-email.me>
In reply to#15720
On 10-Jan-12 17:43, Bill Reid wrote:
> On Jan 10, 9:21 am, Stephen Sprunk <step...@sprunk.org> wrote:
>> On 10-Jan-12 08:47, Bill Reid wrote:
>>> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
>>> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
>>> USENET!!!!!!!
>>>
>>> The answer is that it doesn't matter, your odds are still one
>>> in three no matter what you do...but wait, does it matter if the
>>> presenter knows what's behind the doors and shows you the goat
>>> to make the game more interesting?  Let's see what happens with
>>> the "regs" here, might be fun...
>>
>> Mythbusters recently tested this.  You're always better off switching.
>>
> Did they use a Monte Carlo simulation where they fired cannonballs
> through the garage doors of dozens of innocent people to see whether
> there was a goat or car in the garage?

They did a Monte Carlo simulation, but unfortunately nothing was
destroyed in the process.

I prefer the mathematical proof, but that doesn't make for good TV.

> You're always better off switching, EXCEPT if the presenter knows
> you've chosen the car and ONLY offers you a different door to
> potentially keep you from winning the car.

Their test scenario was that the presenter _always_ opens a losing door,
which they said is how the actual game show worked.

They also first tested how often people switched after that door was
opened; interestingly, zero (of twenty) contestants did so.

S


-- 
Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking

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#15725

FromSeebs <usenet-nospam@seebs.net>
Date2012-01-11 05:00 +0000
Message-ID<slrnjgq5rk.255i.usenet-nospam@guild.seebs.net>
In reply to#15724
On 2012-01-11, Stephen Sprunk <stephen@sprunk.org> wrote:
> Their test scenario was that the presenter _always_ opens a losing door,
> which they said is how the actual game show worked.

They are wrong, I'm pretty sure.  One of the discussions of this included
an interview with the guy, and there was no such rule.

-s
-- 
Copyright 2011, all wrongs reversed.  Peter Seebach / usenet-nospam@seebs.net
http://www.seebs.net/log/ <-- lawsuits, religion, and funny pictures
http://en.wikipedia.org/wiki/Fair_Game_(Scientology) <-- get educated!
I am not speaking for my employer, although they do rent some of my opinions.

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#15727

FromKaz Kylheku <kaz@kylheku.com>
Date2012-01-11 06:32 +0000
Message-ID<20120110222916.331@kylheku.com>
In reply to#15725
On 2012-01-11, Seebs <usenet-nospam@seebs.net> wrote:
> On 2012-01-11, Stephen Sprunk <stephen@sprunk.org> wrote:
>> Their test scenario was that the presenter _always_ opens a losing door,
>> which they said is how the actual game show worked.
>
> They are wrong, I'm pretty sure.  One of the discussions of this included
> an interview with the guy, and there was no such rule.

But odds are 2/3 that he lied in that interview.

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#15744

FromJames Kuyper <jameskuyper@verizon.net>
Date2012-01-11 07:22 -0500
Message-ID<jejuu8$gf8$1@dont-email.me>
In reply to#15725
On 01/11/2012 12:00 AM, Seebs wrote:
> On 2012-01-11, Stephen Sprunk <stephen@sprunk.org> wrote:
>> Their test scenario was that the presenter _always_ opens a losing door,
>> which they said is how the actual game show worked.
> 
> They are wrong, I'm pretty sure.  One of the discussions of this included
> an interview with the guy, and there was no such rule.
> 
> -s
<http://en.wikipedia.org/wiki/Monty_Hall_problem> contains a section
titled "extended problem description" which fills out the unstated
assumptions behind the original statement of the problem. There's a fair
number of them.
There's also a section titled "other host behaviors" which summarizes
the results when other assumptions are made.
-- 
James Kuyper

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#15788

Fromfalk@rahul.net (Edward A. Falk)
Date2012-01-12 22:51 +0000
Message-ID<jeno56$au6$1@blue-new.rahul.net>
In reply to#15720
In article <5a07f9e0-4011-45cb-aec3-0c9c7f888d1e@f11g2000yql.googlegroups.com>,
Bill Reid  <hormelfree@gmail.com> wrote:
>>
>Did they use a Monte Carlo simulation where they fired cannonballs
>through the garage doors of dozens of innocent people to see whether
>there was a goat or car in the garage?

A friend of mine had this to say about that:

  Well, if nothing else,
  they've disproved the myth that 
  suburban houses are safe from 
  cannon attack.

  That's something, anyway....
-- 
	-Ed Falk, falk@despams.r.us.com
	http://thespamdiaries.blogspot.com/

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#15790

FromIan Collins <ian-news@hotmail.com>
Date2012-01-13 12:14 +1300
Message-ID<9n97qeFh5bU1@mid.individual.net>
In reply to#15788
On 01/13/12 11:51 AM, Edward A. Falk wrote:
> In article<5a07f9e0-4011-45cb-aec3-0c9c7f888d1e@f11g2000yql.googlegroups.com>,
> Bill Reid<hormelfree@gmail.com>  wrote:
>>>
>> Did they use a Monte Carlo simulation where they fired cannonballs
>> through the garage doors of dozens of innocent people to see whether
>> there was a goat or car in the garage?
>
> A friend of mine had this to say about that:
>
>    Well, if nothing else,
>    they've disproved the myth that
>    suburban houses are safe from
>    cannon attack.
>
>    That's something, anyway....

That would depend on the construction of the house and the size of the 
cannon.  Mine would fail, but some neighbouring houses (built with 
reinforced block) would survive a significant pounding (or, as recent 
events have shown, significant earthquakes!).

-- 
Ian Collins

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#15794

FromImpalerCore <jadill33@gmail.com>
Date2012-01-12 15:17 -0800
Message-ID<daaea009-ee43-463e-bc9b-66ec56231155@t13g2000vbt.googlegroups.com>
In reply to#15788
On Jan 12, 5:51 pm, f...@rahul.net (Edward A. Falk) wrote:
> In article <5a07f9e0-4011-45cb-aec3-0c9c7f888...@f11g2000yql.googlegroups.com>,
> Bill Reid  <hormelf...@gmail.com> wrote:
>
>
>
> >Did they use a Monte Carlo simulation where they fired cannonballs
> >through the garage doors of dozens of innocent people to see whether
> >there was a goat or car in the garage?
>
> A friend of mine had this to say about that:
>
>   Well, if nothing else,
>   they've disproved the myth that
>   suburban houses are safe from
>   cannon attack.
>
>   That's something, anyway....

And the myth that cannonballs don't bounce.

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#15697

FromShao Miller <sha0.miller@gmail.com>
Date2012-01-10 14:33 -0500
Message-ID<jei3sp$bir$1@dont-email.me>
In reply to#15684
On 1/10/2012 09:47, Bill Reid wrote:
> On Jan 9, 8:56 pm, divya bisht<bisht88.di...@gmail.com>  wrote:
>>
>> You are on a game show and there are three doors. The presenter tells
>> you that behind one of doors there is a car and behind the other two
>> are goats, if you pick the car you win it. After you have picked a
>> door the presenter opens a different door with a goat behind it, he
>> then gives you the chance to change what door you open, what should
>> you do?
>>
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
>

One can download the following book "Information Theory, Inference, and 
Learning Algorithms" by David J. C. MacKay from his site:

   http://www.inference.phy.cam.ac.uk/mackay/itila/

Or better yet, one can purchase it and have it shipped.

This problem is discussed on page 57, exercise 3.8, if I'm not mistaken.

However, the above-stated details are a little different.

- Shao Miller

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#15723

FromKaz Kylheku <kaz@kylheku.com>
Date2012-01-11 01:44 +0000
Message-ID<20120110171743.392@kylheku.com>
In reply to#15684
On 2012-01-10, Bill Reid <hormelfree@gmail.com> wrote:
> On Jan 9, 8:56 pm, divya bisht <bisht88.di...@gmail.com> wrote:
>>
>> You are on a game show and there are three doors. The presenter tells
>> you that behind one of doors there is a car and behind the other two
>> are goats, if you pick the car you win it. After you have picked a
>> door the presenter opens a different door with a goat behind it, he
>> then gives you the chance to change what door you open, what should
>> you do?
>>
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
>
> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do...but wait, does it matter if the
> presenter knows what's behind the doors and shows you the goat
> to make the game more interesting?  Let's see what happens with
> the "regs" here, might be fun...

I think you an easily solve this by a simple division into cases,
and simple probabilities.

Look Ma, no conditional probability, no Bayes' theorem.


Suppose Monty always reveals the goat. (This builds suspense in the
audience and is good for the show's ratings, which are more important
than whether or not cars are given away.)


There are two cases:

Case 1: (p = 2/3) You picked the goat.

Monty knows that this case is occurring, and reveals to you the other goat! So
you must switch to get the car, and by switching the car is guaranteed.

Case 2: (p = 1/3) You picked the car.

In this case, you must not switch; you're already on the car.
Of course Monty reveals a goat in this case also.


Now you don't know which of these cases you are in. But you do know
that one of these cases requires switching and the other requires
staying and that the one that requires switching occurs with p = 2/3, and the
one that requires staying occurs with p = 1/3.

This essentially translates to "the probability that you must switch in order
to win the car is 2/3", and that translates to "the probability that
the car is behind the door you did not pick in round 1 is 2/3".

If you do not switch, you are betting on being in Case 2, which is p = 1/3: the
same odds as a one-round draw.

If you switch, you are betting that you are in Case 1, where you have p = 2/3
odds, an improvement.



Switching: no brainer.

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