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Tweak155

Lifer
Sep 23, 2003
11,448
262
126
You're missing the words before it.

"You pick box at random. You put your hand in and take a ball from that box at random." Including the word "if" certainly helps for clarification, but it is not required. The randomness is explicitly stated in the question, it doesn't need to be implied.

Once again, if the first ball chosen from the box is not random, there is no way to solve this problem without further information. It is either 2/3 or it is impossible to solve, you can't get 50%.

Hitman, just save yourself the time. Humpy clearly likes to "stir the pot" just like the OP. All you're doing is encouraging him.

Stirring the pot has value, but only for so long. There is clearly enough information in this thread to get to the answer that people are searching for, including there being no answer or more than one answer, answers that don't make sense, and most importantly, the right answer .
 
Reactions: Humpy

paperfist

Diamond Member
Nov 30, 2000
6,517
280
126
www.the-teh.com
Hitman, just save yourself the time. Humpy clearly likes to "stir the pot" just like the OP. All you're doing is encouraging him.

Stirring the pot has value, but only for so long. There is clearly enough information in this thread to get to the answer that people are searching for, including there being no answer or more than one answer, answers that don't make sense, and most importantly, the right answer .

He's not stirring the pot, the posted question is.

You guys are using outside sources to answer a question that is worded differently then the one here. No where that I see does it say pick from 2 boxes. It only says 1 and you guys are ignoring this fact.

But the posted question is rigged as you don't know if you'rein a box with GG or GS.

If you do a reverse image search you'll see about 20 other forums went ape s$&@ over this problem including the body building forum from which the image is from.
 

Humpy

Diamond Member
Mar 3, 2011
4,463
596
126
Once again, if the first ball chosen from the box is not random, there is no way to solve this problem without further information.

What further information would you need?

I'm pretty close to taking the L. I understand how the answer can be 2/3. I understand that the problem would be unsolvable if the silver ball was actually an unknown color.
 

loafbred

Senior member
May 7, 2000
836
58
91
Maybe it is easier to understand if you change the two gold balls to one gold and one bronze, and change the question to the chance of the second draw being gold or bronze after the first draw is either gold or bronze.

Then you have B+G and S+G, the chance of drawing S first from the second box is removed, so you are left with B first + G second as option, with G first + B second, and in the second box G first and S second.

So after you draw either a bronze or a gold ball from a chest, how high is the chance of drawing a gold or bronze one again?
This might make it easier to differentiate between the 2 balls in the 'gold box'.

That doesn't help me to understand your belief that the position of the balls in the G+G box, as well as their possible order of removal (only with respect to their position in the box), affect the probability that one will select another gold ball. I appreciate your effort, and I assign no blame to anyone for my dilemma.
 

loafbred

Senior member
May 7, 2000
836
58
91
I need to know first if you're on the 1/2 side or the 2/3 side.
The math demonstrates 2/3, but one can rationally argue 1/2 (yes, while taking all events into account). I started out arguing for 1/2, then accepted 2/3, but am presently agnostic.
 

Tweak155

Lifer
Sep 23, 2003
11,448
262
126
He's not stirring the pot, the posted question is.

You guys are using outside sources to answer a question that is worded differently then the one here. No where that I see does it say pick from 2 boxes. It only says 1 and you guys are ignoring this fact.

But the posted question is rigged as you don't know if you'rein a box with GG or GS.

If you do a reverse image search you'll see about 20 other forums went ape s$&@ over this problem including the body building forum from which the image is from.

Yes because lots of people have trouble grasping something counter intuitive. I would be more shocked if there weren't lots of forums going crazy (assuming it was posted on other forums). That is part of why people post it...
 
Reactions: paperfist

Tweak155

Lifer
Sep 23, 2003
11,448
262
126
The math demonstrates 2/3, but one can rationally argue 1/2 (yes, while taking all events into account). I started out arguing for 1/2, then accepted 2/3, but am presently agnostic.
If you feel the math demonstrates 2/3, then there is no way you should believe that one can rationally argue 1/2. That is part of the beauty of math, it is not refutable.
 

DigDog

Lifer
Jun 3, 2011
13,622
2,189
126
You're missing the words before it.

"You pick box at random. You put your hand in and take a ball from that box at random." Including the word "if" certainly helps for clarification, but it is not required. The randomness is explicitly stated in the question, it doesn't need to be implied.

... no .... no.
 

DigDog

Lifer
Jun 3, 2011
13,622
2,189
126
If you feel the math demonstrates 2/3, then there is no way you should believe that one can rationally argue 1/2. That is part of the beauty of math, it is not refutable.
The math isnt wrong; its just math from a different experiment.
 
Oct 20, 2005
10,978
44
91
The math demonstrates 2/3, but one can rationally argue 1/2 (yes, while taking all events into account). I started out arguing for 1/2, then accepted 2/3, but am presently agnostic.

That is a great answer honestly

What I was trying to answer again? Oh right the different outcomes. I mean it's pretty clear that you literally can pick gold ball #1, then gold ball #2 - OR - gold ball #2 first, then gold ball #1. They are individually different events/outcomes, outcomes which play into the overall probability of what will be picked next.
 

ewdotson

Golden Member
Oct 30, 2011
1,295
1,520
136
Bertrand: so, you have these boxes.
You: ok.
Bertrand: and one has a silver ball in it.
You: ok.
Bertrand: and you draw a ball.
You: ok i draw the silver ball.
Bertrand: no that cannot happen.
You: i am not allowed to draw the silver ball?
Bertrand: no, this experiment exists in a reality where you are not allowed to draw silver.
You: ok.
Bertrand: now calculate the possibilities.
You: this much.
Bertrand: Aha! You fool, you didnt consider the possibility of drawing silver!!
You: ...
That's not what's being said at *all*.

The irony here is that you seem to be the one answering a different question than the one that is asked. So far as I can tell, you're answering what the odds are of selecting the box with two gold balls at the start. That's not actually mathematically equivalent to asking what the odds are of your having selected the box with two gold balls if the first ball you drew was gold. The relevant states are:

S+G2G3
SG1+G2
SG1+G3
 

repoman0

Diamond Member
Jun 17, 2010
4,544
3,471
136
How is this 16 pages? The question posed in the pic is: find P(second ball is gold | first ball is gold). The language is clear, it's just posing that conditional probability problem, which has a clearly defined solution. It's 2/3, end of story
 

aigomorla

CPU, Cases&Cooling Mod PC Gaming Mod Elite Member
Super Moderator
Sep 28, 2005
20,882
3,230
126
The language is clear, it's just posing that conditional probability problem, which has a clearly defined solution. It's 2/3, end of story

Actually its sort of not, because it states you already pulled a gold ball from the box..
The odds of you pulling another gold ball from the same box would mean your odds in the first box with double gold balls out of the boxes with a gold ball.

So your doing P on the boxes itself and not the balls which is the riddle.

Ie... You already pulled a gold ball, meaning, you got (b1 or b2), and out of the 2 you have a 50% chance of selecting the box with the double gold balls, because there is a 0% chance of you getting a second gold ball from the other one, and the box with all silver is to throw you off and confuse you, as its not relevant at all due to the fact you pulled a gold ball to begin with.
 
Last edited:

repoman0

Diamond Member
Jun 17, 2010
4,544
3,471
136
Actually its sort of not, because it states you already pulled a gold ball from the box..
The odds of you pulling another gold ball from the same box would mean you got the first box with double gold balls to begin with.

So your doing P on the boxes itself and not the balls.

Ie... you have a 50% chance of selecting the box with the double gold balls, because there is a 0% chance of you getting a second gold ball from the other 2.

That's not how conditional probability works. The fact that you observed a gold makes it more likely in the first place that you picked from box GG.

You can easily calculate P(second ball is gold | first ball is gold) with Bayes theorem. It's 2/3.
 

aigomorla

CPU, Cases&Cooling Mod PC Gaming Mod Elite Member
Super Moderator
Sep 28, 2005
20,882
3,230
126
you cant use bayes therom on this, because B = 0

The Second BOX has a 0 % chance of it being the solution.
So your looking at a straight probabilty of you selecting the First box when looking at all the boxes with gold.

The balls are whats confusing you, and tripping you out.

The answer to this question is only the box with GG..
Out of the 3, only 2 have G.
So your looking at out of the 2 which one has GG.

50% your got the box with GG, because the other box is 0% your going to get GG.

Here it was answered by Skorpio.
 

Hitman928

Diamond Member
Apr 15, 2012
5,622
8,847
136
What further information would you need?

I'm pretty close to taking the L. I understand how the answer can be 2/3. I understand that the problem would be unsolvable if the silver ball was actually an unknown color.

You would need to know the probability of picking each box as well as each ball inside the box. In the question it is stated that they are random, but if this is not the case, you need to know what the actual probability is.
 

repoman0

Diamond Member
Jun 17, 2010
4,544
3,471
136
B is not 0. Perhaps you should state in probability notation what you think the problem is asking, because my notation has a clear solution.

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

A - both gold
B - first ball is gold

So we have P(both gold | first ball is gold), or in English probability that both balls are gold given that you observe a gold ball after the first pick.

P(A) = P(both gold) = 1/3 -- one out of three boxes has both gold
P(B) = P(first ball is gold) = P(first ball gold | both gold) * P(both gold) + P(first ball gold | both silver) * P(both silver) + (first ball gold | one of each) * P(one of each) = 1 * 1/3 + 0 * 1/3 + 1/2 * 1/3 -- summing up conditional probabilities to get P(B)
P(B|A) = P(first ball gold | both gold) = 1

1 * 1/3 / (1/3 + 1/6) = 2/3

I don't want to see any silly explanation pictures, I want to see the math.

you cant use bayes therom on this, because B = 0

The Second BOX has a 0 % chance of it being the solution.
So your looking at a straight probabilty of you selecting the First box when looking at all the boxes with gold.

The balls are whats confusing you, and tripping you out.

The answer to this question is only the box with GG..
Out of the 3, only 2 have G.
So your looking at out of the 2 which one has GG.

50% your got the box with GG, because the other box is 0% your going to get GG.

Here it was answered by Skorpio.
 

aigomorla

CPU, Cases&Cooling Mod PC Gaming Mod Elite Member
Super Moderator
Sep 28, 2005
20,882
3,230
126
P(A) = P(both gold) = 1/3 -- one out of three boxes has both gold

no because your not even looking at the third box.
You already pulled a gold ball from a box.
That means it was already determined you got either box 1 or 2 without probability.

So your looking at 2 boxes.
The odds of you getting the box with GG out of the 2 boxes is what?
50%?

lol... read the question carefully, your overthinking the problem.

A better title for this should be people with an IQ under 115 can answer this problem, because i honestly feel if your IQ is too high, you will overthink it.
 

Hitman928

Diamond Member
Apr 15, 2012
5,622
8,847
136
you cant use bayes therom on this, because B = 0

The Second BOX has a 0 % chance of it being the solution.
So your looking at a straight probabilty of you selecting the First box when looking at all the boxes with gold.

The balls are whats confusing you, and tripping you out.

The answer to this question is only the box with GG..
Out of the 3, only 2 have G.
So your looking at out of the 2 which one has GG.

50% your got the box with GG, because the other box is 0% your going to get GG.

Here it was answered by Skorpio.

You do realize that Skorpio later in the thread stated that he was wrong in that answer and that it is 2/3, right? So you're using an answer the author already said was in error.

As far as solving the probability, you absolutely can use Baye's Theorem.

 

repoman0

Diamond Member
Jun 17, 2010
4,544
3,471
136
You do realize that Skorpio later in the thread stated that he was wrong in that answer and that it is 2/3, right? So you're using an answer the author already said was in error.

As far as solving the probability, you absolutely can use Baye's Theorem.


Hey how about that! Wiki stole my answer
 

repoman0

Diamond Member
Jun 17, 2010
4,544
3,471
136
no because your not even looking at the third box.
You already pulled a gold ball from a box.
That means it was already determined you got either box 1 or 2 without probability.

So your looking at 2 boxes.
The odds of you getting the box with GG out of the 2 boxes is what?
50%?

lol... read the question carefully, your overthinking the problem.

A better title for this should be people with an IQ under 115 can answer this problem, because i honestly feel if your IQ is too high, you will overthink it.

That is literally taken into account right there in the P(B) calculation. P(first ball gold | both silver) = 0.
 
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