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#52 Apr 01 2008 at 11:33 AM Rating: Good
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OK, take a look at this from simple math. There are 3 doors, you subtract one away. Now there are 2. What is the chance that you pick the right door now? This is the perspective I'm talking about. From this snapshot, where there are only 2 doors, you have a 50/50 shot of getting it right.

No, you never truly have a 50% chance in any part of the full equation, but in this one frame of it, you do. That's what Tarv was saying.
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#53 Apr 01 2008 at 11:51 AM Rating: Decent
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Lets look at this from the top.

3 doors, one has a prize, the others are empty. The odds are extremely clear: you have a 1/3 chance of choosing the correct door.

You pick a door. It has 33% chance of being a winner.

The host opens a door that you didn't pick, revealing an empty door.

Does your door still have a 33% chance of winning? NO. It does not, because the equation isn't valid anymore. He gives you the option of switching doors. So now, armed with this knowledge, you are looking at the following situation:

2 doors, one has a prize, the other is empty. The odds are still extremely clear: you have a 1/2 chance of choosing the correct door.

I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.
#54 Apr 01 2008 at 12:13 PM Rating: Good
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AshOnMyTomatoes, Guardian of the Glade wrote:
I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.
It only doesn't matter if you disregard previous knowledge, then you have a 50/50 chance.
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#55 Apr 01 2008 at 12:15 PM Rating: Good
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Uglysasquatch, Mercenary Major wrote:
AshOnMyTomatoes, Guardian of the Glade wrote:
I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.
It only doesn't matter if you disregard previous knowledge, then you have a 50/50 chance.
That's the point: previous knowledge no longer applies.
#56 Apr 01 2008 at 12:15 PM Rating: Good
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So... now we know who here failed math.
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#57 Apr 01 2008 at 12:16 PM Rating: Decent
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Think about it this way if you had a million doors with 1 car and 999,999 goats. you pick a door at random the host (who knows where the car is) opens 999,998 other doors revealing all goats

This is the exact same problem just on a grander scale. The odds of you having initially picked the car are 1 in a million and the odds of you getting the car if you swap are now 999,999 in a million.

Smiley: nod Previous knowledge clearly applies

Edited, Apr 1st 2008 4:17pm by SWM
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#58 Apr 01 2008 at 12:16 PM Rating: Decent
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Timelordwho wrote:
So... now we know who here failed math.
You can be a ******* genius in math and still not understand how it applies to an everyday situation. This situation is a perfect case in point. Smiley: tongue
#59 Apr 01 2008 at 12:18 PM Rating: Good
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SWM wrote:
Think about it this way if you had a million doors with 1 car and 999,999 goats. you pick a door at random the host (who knows where the car is) opens 999,998 other doors revealing all goats

This is the exact same problem just on a grander scale. The odds of you having initially picked the car are 1 in a million and the odds of you getting the car if you swap are now 999,999 in a million.

Smiley: nod Previous knowledge clearly applies

Edited, Apr 1st 2008 4:17pm by SWM
That is, in fact the exact same situation. And you do now still have a 50/50 chance. You can add as many zeros to the end of that as you like.
#60 Apr 01 2008 at 12:19 PM Rating: Decent
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AshOnMyTomatoes, Guardian of the Glade wrote:
I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.


No, 2/3rds is the correct answer. Take the graphical example of all possibilities, part of which was shown in an earlier post. 2/3rds of those possibilities ends with you winning a car.

 
You choose Door Number 1. 
[o] [x] [x]  You change, you lose.  Total So Far: 0/1 
[x] [o] [x]  You change, you win.   Total So Far: 1/2 
[x] [x] [o]  You change, you win.   Total So Far: 2/3 
 
You choose Door Number 2.  
[o] [x] [x]  You Change, you win.   Total So Far: 3/4 
[x] [o] [x]  You Change, you lose.  Total So Far: 3/5 
[x] [x] [o]  You Change, you win.   Total So Far: 4/6 
 
You choose Door Number 3. 
[o] [x] [x]  You Change, you win.   Total So Far: 5/7 
[x] [o] [x]  You Change, you win.   Total So Far: 6/8 
[x] [x] [o]  You Change, you lose.  Total So Far: 6/9 


As you can see, out of all the possible outcomes when you change your door, you end up with 6 winning outcomes out of 9 total.

6 chances of winning outta 9 is a 2/3rds possibility of winning if you change your mind.
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#61 Apr 01 2008 at 12:21 PM Rating: Decent
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TirithRR if I wasnt convinced before then I sure am now.
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#62 Apr 01 2008 at 12:22 PM Rating: Good
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TirithRR the Mundane wrote:
AshOnMyTomatoes, Guardian of the Glade wrote:
I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.


No, 2/3rds is the correct answer. Take the graphical example of all possibilities, part of which was shown in an earlier post. 2/3rds of those possibilities ends with you winning a car.

 
You choose Door Number 1. 
[o] [x] [x]  You change, you lose.  Total So Far: 0/1 
[x] [o] [x]  You change, you win.   Total So Far: 1/2 
[x] [x] [o]  You change, you win.   Total So Far: 2/3 
 
You choose Door Number 2.  
[o] [x] [x]  You Change, you win.   Total So Far: 3/4 
[x] [o] [x]  You Change, you lose.  Total So Far: 3/5 
[x] [x] [o]  You Change, you win.   Total So Far: 4/6 
 
You choose Door Number 3. 
[o] [x] [x]  You Change, you win.   Total So Far: 5/7 
[x] [o] [x]  You Change, you win.   Total So Far: 6/8 
[x] [x] [o]  You Change, you lose.  Total So Far: 6/9 


As you can see, out of all the possible outcomes when you change your door, you end up with 6 winning outcomes out of 9 total.

6 chances of winning outta 9 is a 2/3rds possibility of winning if you change your mind.
Ah, some data to work with. This is assuming which door was opened, and which door had the winning prize to start with?
#63 Apr 01 2008 at 12:23 PM Rating: Good
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TirithRR if I wasnt convinced before then I sure am now.
I'm not, and I can prove it with Tirith's help.
#64 Apr 01 2008 at 12:24 PM Rating: Good
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AshOnMyTomatoes, Guardian of the Glade wrote:
Ah, some data to work with. This is assuming which door was opened, and which door had the winning prize to start with?


This is all possibilities of door selections and prize locations.

Edit: With 3 doors, and one prize that is.

Edited, Apr 1st 2008 4:25pm by TirithRR
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#65 Apr 01 2008 at 12:26 PM Rating: Good
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Stop rating me down for working through some goddamn math and logic, you supercilious pricks.Smiley: mad

Whoever you are.
#66 Apr 01 2008 at 12:26 PM Rating: Good
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TirithRR: You could have just redirected them to my post earlier in the thread Smiley: mad

Ash...you are either doing an excellent job trolling, or you clearly don't know what the **** you are talking about.
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#67 Apr 01 2008 at 12:28 PM Rating: Good
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Timelordwho wrote:
TirithRR: You could have just redirected them to my post earlier in the thread Smiley: mad

Ash...you are either doing an excellent job trolling, or you clearly don't know what the @#%^ you are talking about.


I mentioned your post... indirectly. I just couldn't remember who wrote it. I merely expanded on it to show all the possible outcomes, to try and show beyond a doubt that it was true.


Edit:

Basically, it boils down to this:

If you ignore the fact that there were 3 doors, and say that it's now only a 50/50, 2 door problem, you are forgetting the fact that there were two different goats for you to originally choose. Choose either of the two goats, and you win, choose the car, and you lose.

Changing your mind swaps the probability the outcome. You have to choose wrong first in order to win.

Edited, Apr 1st 2008 4:40pm by TirithRR
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#68 Apr 01 2008 at 12:39 PM Rating: Excellent
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AshOnMyTomatoes, Guardian of the Glade wrote:
Stop rating me down for working through some goddamn math and logic, you supercilious pricks.Smiley: mad

Whoever you are.


Seriously. They're just pissed because they picked goats. Smiley: laugh

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#69 Apr 01 2008 at 12:41 PM Rating: Decent
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TirithRR the Mundane wrote:
AshOnMyTomatoes, Guardian of the Glade wrote:
I don't care what fancy math you want to apply to it. It doesn't matter whether you switch doors or not, that '2/3rds' odds of you having chosen the incorrect door does not apply to the new situation.


No, 2/3rds is the correct answer. Take the graphical example of all possibilities, part of which was shown in an earlier post. 2/3rds of those possibilities ends with you winning a car.

 
You choose Door Number 1. 
[o] [x] [x]  You change, you lose.  Total So Far: 0/1 
[x] [o] [x]  You change, you win.   Total So Far: 1/2 
[x] [x] [o]  You change, you win.   Total So Far: 2/3 
 
You choose Door Number 2.  
[o] [x] [x]  You Change, you win.   Total So Far: 3/4 
[x] [o] [x]  You Change, you lose.  Total So Far: 3/5 
[x] [x] [o]  You Change, you win.   Total So Far: 4/6 
 
You choose Door Number 3. 
[o] [x] [x]  You Change, you win.   Total So Far: 5/7 
[x] [o] [x]  You Change, you win.   Total So Far: 6/8 
[x] [x] [o]  You Change, you lose.  Total So Far: 6/9 


As you can see, out of all the possible outcomes when you change your door, you end up with 6 winning outcomes out of 9 total.

6 chances of winning outta 9 is a 2/3rds possibility of winning if you change your mind.
Ok I think I found the problem with your model. It doesn't take into account the fact that the opened door was definitely a loser. AND the fact that the host CAN'T open a door that is a winner, or the door you chose initially.

Lets see: (we'll have a door that the host can't open represented in bold.)

You choose door 1:

[o] [x] [x] Door 3 is opened. You change, you lose.
Door 2 is opened. You change, you lose.
[x] [o] [x] Door 3 is opened. You change, you win.
[x] [x] [o] Door 2 is opened. You change, you win.

You choose door 2:

[o] [x] [x] Door 3 is opened. You change, you win.
[x] [o] [x] Door 1 is opened. You change, you lose.
Door 3 is opened. You change, you lose.
[x] [x] [o] Door 1 is opened. You change, you win.

You choose door 3:

[o] [x] [x] Door 2 is opened. You change, you win.
[x] [o] [x] Door 1 is opened. You change, you win.
[x] [x] [o] Door 1 is opened. You change, you lose.
Door 2 is opened. You change, you lose.

Your chart leaves out a few possible scenarios.
#70 Apr 01 2008 at 12:43 PM Rating: Good
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Uglysasquatch, Mercenary Major wrote:
It is if you just take a snapshot in time, which is what Tarv's doing. Technically, you're right. But once you eliminate one door and then forget it existed, you're left with 2 choices. At this point, you're first guess has as likely a chance of winning as changing does.

But that would be missing the entire point of this puzzle? The point is you do know that there were three doors and that one of the wrong doors was removed, now how can you use this information to your advantage.

What you are arguing is correct, but none of it applies because the given situation is not the one your argument is based on. There is no forgetting of previous information in this situation; there is no snapshot in time.
#71 Apr 01 2008 at 12:48 PM Rating: Good
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Someone didn't like my glaringly obvious logic.Smiley: laugh
#72 Apr 01 2008 at 12:49 PM Rating: Good
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AshOnMyTomatoes, Guardian of the Glade wrote:
Your chart leaves out a few possible scenarios.


While it may seem that way, it's not.

The only thing that matters is what door you choose, and whether or not you change. It doesn't matter what the door is that the game host picks.

If you choose the winning door originally, and change, you lose. You cannot count that twice, cause it's the same scenario.


The Possibilities are:
If you choose one of the two losing doors, and change, you win.
If you choose the other of the two losing doors, and change, you win.
If you choose the winning door, and change, you lose.

If you decide in the beginning that are you are going to change your mind, then you must choose a goat first to win, which gives you a 66.667% chance of winning.

Edited, Apr 1st 2008 4:50pm by TirithRR
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#73 Apr 01 2008 at 12:51 PM Rating: Excellent
AshOnMyTomatoes, Guardian of the Glade wrote:
Someone didn't like my glaringly obvious logic.Smiley: laugh


I rated you back up. I don't understand this thread, and I'm having horrible flash backs to statistics, but it looked smart.
#74 Apr 01 2008 at 12:52 PM Rating: Good
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TirithRR the Mundane wrote:
If you choose the winning door originally, and change, you lose. You cannot count that twice, cause it's the same scenario.


The Possibilities are:
If you choose one of the two losing doors, and change, you win.
If you choose the other of the two losing doors, and change, you win.
If you choose the winning door, and change, you lose.
By this logic, it doesn't matter which of the losing doors you picked, because the outcome is also the same. Which would revise your above list to:

The Possibilities are:
If you choose one of the two losing doors, and change, you win.
If you choose the winning door, and change, you lose.
#75 Apr 01 2008 at 12:54 PM Rating: Excellent
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TirithRR the Mundane wrote:
The Possibilities are:
If you choose one of the two losing doors, and change, you win.
If you choose the other of the two losing doors, and change, you win.
If you choose the winning door, and change, you lose.

If you decide in the beginning that are you are going to change your mind, then you must choose a goat first to win, which gives you a 66.667% chance of winning.

If you choose one of the two losing doors and change to the other losing door, you still lose.

It's not a 66.66% chance of winning.

Unless I've misread somewhere and by "changing" you mean pick the opposite of whatever outcome you've just chosen.
#76 Apr 01 2008 at 12:54 PM Rating: Good
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Prince Kaain wrote:
TirithRR the Mundane wrote:
The Possibilities are:
If you choose one of the two losing doors, and change, you win.
If you choose the other of the two losing doors, and change, you win.
If you choose the winning door, and change, you lose.

If you decide in the beginning that are you are going to change your mind, then you must choose a goat first to win, which gives you a 66.667% chance of winning.

If you choose one of the two losing doors and change to the other losing door, you still lose.

It's not a 66.66% chance of winning.

Unless I've misread somewhere and by "changing" you mean pick the opposite of whatever outcome you've just chosen.
You can't change to the other losing door, because the host has opened it.
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