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Groups > comp.lang.c > #15684 > unrolled thread
| Started by | Bill Reid <hormelfree@gmail.com> |
|---|---|
| First post | 2012-01-10 06:47 -0800 |
| Last post | 2012-01-14 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 →
| From | Bill Reid <hormelfree@gmail.com> |
|---|---|
| Date | 2012-01-10 06:47 -0800 |
| Subject | Re: 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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| From | tom st denis <tom@iahu.ca> |
|---|---|
| Date | 2012-01-10 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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| From | falk@rahul.net (Edward A. Falk) |
|---|---|
| Date | 2012-01-11 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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| From | Eric Sosman <esosman@ieee-dot-org.invalid> |
|---|---|
| Date | 2012-01-10 11:23 -0500 |
| Message-ID | <jehole$5o6$1@dont-email.me> |
| In reply to | #15684 |
On 1/10/2012 9:47 AM, Bill Reid wrote:
> On Jan 9, 8:56 pm, divya bisht<bisht88.di...@gmail.com> wrote:
>>
>> You are on a game show and there are three doors. The presenter tells
>> you that behind one of doors there is a car and behind the other two
>> are goats, if you pick the car you win it. After you have picked a
>> door the presenter opens a different door with a goat behind it, he
>> then gives you the chance to change what door you open, what should
>> you do?
>>
> OH NO, THE DREADED "MONTY HALL" PROBLEM, IT'S BEEN AT LEAST A
> DECADE SINCE I'VE SEEN THIS MONSTROUSITY REAR IT'S UGLY HEAD IN
> USENET!!!!!!!
>
> The answer is that it doesn't matter, your odds are still one
> in three no matter what you do...but wait, does it matter if the
> presenter knows what's behind the doors and shows you the goat
> to make the game more interesting? Let's see what happens with
> the "regs" here, might be fun...
Stick with the original choice. You can't eat a car.
--
Eric Sosman
esosman@ieee-dot-org.invalid
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| From | John Gordon <gordon@panix.com> |
|---|---|
| Date | 2012-01-10 16:48 +0000 |
| Message-ID | <jehq41$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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| From | Seebs <usenet-nospam@seebs.net> |
|---|---|
| Date | 2012-01-10 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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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Date | 2012-01-10 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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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Date | 2012-01-10 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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| From | Seebs <usenet-nospam@seebs.net> |
|---|---|
| Date | 2012-01-10 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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| From | Stephen Sprunk <stephen@sprunk.org> |
|---|---|
| Date | 2012-01-10 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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| From | Bill Reid <hormelfree@gmail.com> |
|---|---|
| Date | 2012-01-10 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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| From | Stephen Sprunk <stephen@sprunk.org> |
|---|---|
| Date | 2012-01-10 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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| From | Seebs <usenet-nospam@seebs.net> |
|---|---|
| Date | 2012-01-11 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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| From | Kaz Kylheku <kaz@kylheku.com> |
|---|---|
| Date | 2012-01-11 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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| From | James Kuyper <jameskuyper@verizon.net> |
|---|---|
| Date | 2012-01-11 07:22 -0500 |
| Message-ID | <jejuu8$gf8$1@dont-email.me> |
| In reply to | #15725 |
On 01/11/2012 12:00 AM, Seebs wrote: > On 2012-01-11, Stephen Sprunk <stephen@sprunk.org> wrote: >> Their test scenario was that the presenter _always_ opens a losing door, >> which they said is how the actual game show worked. > > They are wrong, I'm pretty sure. One of the discussions of this included > an interview with the guy, and there was no such rule. > > -s <http://en.wikipedia.org/wiki/Monty_Hall_problem> contains a section titled "extended problem description" which fills out the unstated assumptions behind the original statement of the problem. There's a fair number of them. There's also a section titled "other host behaviors" which summarizes the results when other assumptions are made. -- James Kuyper
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| From | falk@rahul.net (Edward A. Falk) |
|---|---|
| Date | 2012-01-12 22:51 +0000 |
| Message-ID | <jeno56$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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| From | Ian Collins <ian-news@hotmail.com> |
|---|---|
| Date | 2012-01-13 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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| From | ImpalerCore <jadill33@gmail.com> |
|---|---|
| Date | 2012-01-12 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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| From | Shao Miller <sha0.miller@gmail.com> |
|---|---|
| Date | 2012-01-10 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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| From | Kaz Kylheku <kaz@kylheku.com> |
|---|---|
| Date | 2012-01-11 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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