Three Curtains

  • Christian Chat is a moderated online Christian community allowing Christians around the world to fellowship with each other in real time chat via webcam, voice, and text, with the Christian Chat app. You can also start or participate in a Bible-based discussion here in the Christian Chat Forums, where members can also share with each other their own videos, pictures, or favorite Christian music.

    If you are a Christian and need encouragement and fellowship, we're here for you! If you are not a Christian but interested in knowing more about Jesus our Lord, you're also welcome! Want to know what the Bible says, and how you can apply it to your life? Join us!

    To make new Christian friends now around the world, click here to join Christian Chat.
posthuman

posthuman

Senior Member
#21
Jul 31, 2013
37,948
13,615
113
#21
rstrats said:
You are a contestant on a game show. There are three curtains. Behind one of the curtains is a new car. You are asked to choose one of the curtains. Lets say that you choose curtain #1. The host of the show - who knows where the car is so as not to end the game prematurely - opens curtain #3 and there is no car behind it. The host now gives you a choice. You can stay with curtain #1 or you can change your choice to curtain #2. The question now is: would it be to your advantage to stay with curtain #1, or would it be to your advantage to change to curtain #2 or would there be no advantage either way?
Click to expand...
You have a mathematically greater probability of success if you change your guess to curtain #2 after curtain 3 is revealed to not have the prize.
 
posthuman

posthuman

Senior Member
#22
Jul 31, 2013
37,948
13,615
113
#22
Lynx said:
Those odds go somewhere though. They don't just disappear. Specifically, half the odds go to each of the remaining doors.
Click to expand...
Essentially, the odds don't change.
You picked one door with 1/3 chance of success - the doors you didn't pick have 2/3 chance of success.

When one of the other 2 is revealed as not-success, there's still 2/3 chance your first guess was wrong but the alternative has been collapsed to only one other door. That other door has the whole other 2/3 chance now.
 
posthuman

posthuman

Senior Member
#23
Jul 31, 2013
37,948
13,615
113
#23
Lynx said:
Not at all. When the host opens #3, it changes the probability of the remaining curtains. Your area B now has a 50/50 chance, not a two thirds chance.
Click to expand...
Learning something about door #3 later doesn't change the odds you originally chose with ;)
 
posthuman

posthuman

Senior Member
#24
Jul 31, 2013
37,948
13,615
113
#24
rstrats said:
What would you do if after your pick of curtain #1, and before any curtains were opened, the host told you that you could change your pick to both curtains #2 and #3?
Click to expand...
That's a really smart question to ask :)
 
christian74

christian74

Senior Member
#25
Oct 1, 2013
594
282
63
#25
posthuman said:
Essentially, the odds don't change.
You picked one door with 1/3 chance of success - the doors you didn't pick have 2/3 chance of success.

When one of the other 2 is revealed as not-success, there's still 2/3 chance your first guess was wrong but the alternative has been collapsed to only one other door. That other door has the whole other 2/3 chance now.
Click to expand...

I knew the answer only because this same question was asked in a movie called '21' (it's about counting cards, Kevin Spacey) but never really understood why until having read your explanation.
 
R

rstrats

Senior Member
#26
Aug 28, 2011
748
43
28
#26
posthuman said:
Essentially, the odds don't change.
.
Click to expand...


Actually, they do. The odds of the car being behind curtain #2 go from 1/3rd to 2/3rds and the odds of the car being behind curtain #3 go from 1/3rd to zero. But try telling Lynx that.
 
You must log in or register to reply here.