Youre wrong on this one mad=dog

This time it's different. We know one side is blue so it's a 50% chance.

If we follow your way:
probability its blue = 1/3 (since only one blue blue coin)
then
probability its red = 1/3 (since there is also only one red coin)
They dont add up to 1.
So it's wrong. Because they have to add up to 1 since there is no other choice. It has to be either blue or red.

[ 06-23-2005, 07:33 PM: Message edited by: ZFR ]

That is correct. Haste makes waste.

EDIT:
... or is it really 50%? The all blue coin contains two identical events as it has two sides. Or in another way.
All events:
RED 1 UP : RED 2 DOWN - 1/6 [Discarded event: Red up]
RED 2 UP : RED 1 DOWN - 1/6 [Discarded event: Red up]
RED UP : BLUE DOWN - 1/6 [Discarded event: Red up]
BLUE UP : RED DOWN - 1/6
BLUE 1 UP : BLUE 2 DOWN - 1/6
BLUE 2 UP : BLUE 1 DOWN - 1/6

Now only 1/3 of the acceptable outcomes have red down....

[ 06-23-2005, 09:41 PM: Message edited by: mad=dog ]

I can't wrap my silly little mind about what everyone is talking about.

I have to side with Q.

It's 50/50 chance. My mind just won't look at it any other way. LoL.

::raises hand:: 'Scuse me... Can we go back to orcs and dwarves? These numbers make my head hurt...

Okay then split the problem.
Once the coin is on the table there is a 50/50 chance of red and blue. But that is half the problem. We also need to actually pick a coin.
The red/blue coin can only be picked with the blue side up whereas the blue/blue coin can be picked with either side up. So the likelihood of the coin being the red/blue is 1/3 and the likelihood of it being the blue/blue coin is 2/3.

Mad=dog, I think you just like the fraction 2/3 [img]tongue.gif[/img]

Youre right mad=dog (in the second and third post regarding coins not the first one). I made a mistake in that one too.

It is 2/3 for blue and 1/3 for red.

P(Blue on other side|Blue on one side)

Call this: P(B|A)

P(B|A)=P(AnB)/P(A)

Can't be bothered to put the numbers in, but that is the formula.

OK here is a different one a la orc and dwarf. Very simple.

You are in the wilderness of Africa and youre lost. Youre guide tells you there are three tribes nearby.
One tribe which worships the sun and always says the truth.
One tribe which worships the moon and always lies.
One tribe which worships the stars and sometimes tells the truth and sometimes lies.

There are three ways and three people, one from each tribe.
The first says: "I do not worship the sun. The proper way is to the west"
The second says: "I do not worship the moon. The proper way is to the east"
The third says: "I do not worship the stars. The proper way is to the south"

Which way do you choose

[ 06-24-2005, 06:04 PM: Message edited by: ZFR ]

<font color = lightgreen> [img]graemlins/erm.gif[/img] I would camp out for the night then figure out which way is east when the sun rises in the morning. I'd make my own way from there. [img]graemlins/petard.gif[/img] </font>