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Topic review (newest first)
- noelevans
- 2012-07-26 04:25:33
Yup! I looked at the Wiki article. But alas I haven't had time to really think about it all. I'm helping a friend move most of today.
- anonimnystefy
- 2012-07-25 23:32:19
I think the probability stays the same in both cases. Did you look at the Wikipeadia article on the Bertrand's box paradox.
- noelevans
- 2012-07-25 23:19:20
Does the original problem state that the marbles are distinguishable or not?
Distinguishability makes a big difference in the way probabilities turn out. Could it be that the 1/2 comes from indistinguishability and the 2/3 from distinuishability? The solution in post #5 appears to assume distinguishability.
Some other important concerns in probability: Repetition vs not, replacement vs not, the sample space for the problem. 
Probability can be exceedingly tricky!
- anonimnystefy
- 2012-07-25 23:03:30
The problem is called Bertrand's box paradox.
There is another neat solution on wikipedia.
- bob bundy
- 2012-07-25 22:17:23
hi Nicholas,
Welcome to the forum!
Do you have a method for generating random events with known probabilities (eg. Excel) ?
If so, then try simulating this a large number of times. Maybe it will help to change your mind.
Or study Bayes Theorem and probability tree diagrams.
Bob
- Nicholas
- 2012-07-25 21:57:17
I agree this answer is wrong it says the answer is 2/3 because you are picking marbles not bags. That answer is if you were picking bags. The probability of you picking a white marble is 3/6 or simplified 1/2.
You have the wrong answer posted.
- MathsIsFun
- 2011-06-14 22:32:19
Are you referring to this: Bags of Marbles - Solution ?
- bobbym
- 2011-06-14 19:29:30
Hi Anne Smith;
Welcome to the forum!
- Anne Smith
- 2011-06-14 18:58:15
I quite agree with your last member. The options are only that it is a white or a black marble, because whether or not you have already selected marble 1 or two from bag A the next outcome is a white anyway.
- bobbym
- 2011-06-01 21:42:39
Hi bobcatfans;
Welcome to the forum.
If you are referring to the Monty Hall problem then switching is definitely favorable. Just tree the problem.
A long time ago Marilyn Vos Savant made a big stir when she caught a bunch of people making a mistake on this problem. The problem first pops up in a statistics journal circa 1958.
- bobcatfans
- 2011-06-01 19:55:54
The solution given for the problem of the white and black marbles is flawed. We are dealing with combinations here and not permutations. Once a white marble is drawn, it doesn't matter if it was the first or second marble. There are only two possible outcomes at this point and therefore the probability is one in two.
The solution for the problem of the goats and new car is similarly flawed. At the point that the one goat is shown, there are only two possibilities remaining. Changing your pick will NOT increase your probability of winning the car. The probability of your original pick DOES change once the one door is opened! 