Puzzle

platypus said:
Indeed. Oldest trick in the book.

You've now got a 2/3 chance to win, rather then 1/3.
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Correct, but that doesn't show the working out of why it's 2/3. This is the part that screws a lot of people up :o

seek said:
Because when you pick you have a 1/3 chance. But if you change it becomes 50/50.

Actually the same applies regardless of the number of doors. It's always better odds to change.
Click to expand...

Sorry, it's not 50/50 :)
 
peetee said:
Hmm just had this puzzle in my emails ... its from a competitor so dont spank me please.

A man was born in 1964 and died in 1984 at the age of 25. How is this possible?

Usually I can get their puzzles but never bother emailing in, Anyone got any idea of this one though?
Click to expand...

Easy. 1984 / 1964 are towns or places

/edit - damn I'm extra slow today!
 
thesubstitute said:
Correct, but that doesn't show the working out of why it's 2/3. This is the part that screws a lot of people up :o
Click to expand...
I can do simple probability, I dont need to show working out :p.

Door 1.
Door 2.
Door 3.

Your initial chances are 1/3, thus you have have a 2/3 chance to be wrong.

With one of the 2 chances of being wrong when the host takes away a wrong door being removed, your fortunes are reversed..
 
Here's a daft one for you then: A man rode into town on Friday, stayed four nights, then left early Sunday morning. Explain.
 
The working out for the doors one is easy....

Initially you pick a door and have a 1/3 chance of being right.

Then the host shows you a 'losing door' the possible outcomes are as follows:

1) You picked the 'right door', the other two are both empty and host can show either
2) You picked 'wrong door 1', the host has to show you 'wrong door 2'
3) you picked 'wrong door 2, the host has to show you 'wrong door 1'

Each of these outcomes is equally likely (1/3) when you picked the door.

After the host has showed you a door, assume you DON'T change...

In 1) you Win!
In 2) you lose
In 3) you lose

Assume you do change

In 1) you lose
In 2) you Win!
In 3) you Win!

So if you change, you win 2 times out of 3!! Whereas if you stick, you only win once ;)
 
thesubstitute said:
Let's start with a classic one:

You have made it to the final round of a game show and you're presented with three doors. Behind one of them is fame, fortune and a white Volvo, there is nothing behind the other two doors.

You pick a door at which point the showhost (who knows what's behind each door) opens one of the other two doors, but he is only allowed to open an empty door.

You now have a choice of whether to stick with the door you originally picked or should you change to the remaining unopened door.

Should you change your mind or stay with your first choice? Or does it matter at all?
Click to expand...

You realise what you've done now?
There will be huge amounts of people who won't accept the answer and will swear blind that it's 50/50 with two doors.

We had a similar thread here: http://forums.overclockers.co.uk/showthread.php?t=17825376
 
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