21 - I am confused

[TimberWolf]

Game 2

door 3

Door 2 has a goat behind it. Do you want to change your mind?

[oracleslave]

Door 2 has a goat behind it. Do you want to change your mind?

yes

[sasguru]

It's a used Aygo with a rubber doll in the passenger seat and a rusted brompton in the back. Can I swap it for a goat?

Crap. Someone stole my car and offered it for a prize in a crappy game show?mad

[TimberWolf]

yes

Which door (I know, but it saves me some effort at this end if you tell me).

[oracleslave]

Which door (I know, but it saves me some effort at this end if you tell me).

Door 1

[TimberWolf]

Door 1

Door 1 has a goat behind it. You win a goat this time.

[TimberWolf]

Game 3

Game 3
Pick a door oracleslave...

[expat]

I still dont get it. Maths was never my strong point. I passed the probability part of the maths exam at Uni, but only by applying the theory and not due to understanding.

He is always going to show me a goat so there is only ever a 50 50 chance that I have chosen the car already.
What has happened before makes no difference as far as I can see.
Dont try and explain it, I have a blind spot here. You will do well if you can make me understand it.

Nothing has changed after the door is opened, that is exactly the point.

When you first pick a door, there is not a 50-50 chance that you have chosen the car, there is 1 chance in 3 that you have chosen the car; and 2 chances in 3 that you have not chosen the car. Then he opens a door. Nothing has changed, physically. There is still only 1 chance in 3 that you have chosen tha car, and 2 chances in 3 that you haven't chosen the car.

What has changed is that the 2 chances in 3 are now embodied in 1 single door.

It's equivalent to saying right at the start, choose either 1 door or 2 doors. Which would you choose?

[oracleslave]

Game 3
Pick a door oracleslave...

Haven't we just proven it is 50/50?

Door 3.

[TimberWolf]

Game 3

Haven't we just proven it is 50/50?

Door 3.

Keep going until you get bored. Are you happy it is 50-50?

Game 3
Door 2 is a goat. Do you want to swap doors?