A fun little probability puzzle for you.

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Flannel Jesus
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A fun little probability puzzle for you.

Post by Flannel Jesus »

Don't look up the answer or read further, try to solve it yourself first.

I present to you 4 USD bills, 1 $1 bill and 3 $100 bills. I then tell you I'm going to put 2 of these bills in one box, and the other 2 in another box - I shut a curtain and do so out of your sight. I then present you with the two boxes.

So, in front of you now are 2 boxes, both apparently identical from the outside, but one has a $1 and a $100 in it, and the other has a $100 and another $100 in it. You don't know which one is which.

Now I say, you may choose a box, so you do so - I put the other box away. I now say, reach inside and grab one of the bills inside the box. You do so, and you find that you've selected a $100.

What is the probability that the other bill remaining in the box you selected is also a $100?
bobmax
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Re: A fun little probability puzzle for you.

Post by bobmax »

66%
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Sculptor
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Re: A fun little probability puzzle for you.

Post by Sculptor »

Flannel Jesus wrote: Sat Jul 16, 2022 7:36 am Don't look up the answer or read further, try to solve it yourself first.

I present to you 4 USD bills, 1 $1 bill and 3 $100 bills. I then tell you I'm going to put 2 of these bills in one box, and the other 2 in another box - I shut a curtain and do so out of your sight. I then present you with the two boxes.

So, in front of you now are 2 boxes, both apparently identical from the outside, but one has a $1 and a $100 in it, and the other has a $100 and another $100 in it. You don't know which one is which.

Now I say, you may choose a box, so you do so - I put the other box away. I now say, reach inside and grab one of the bills inside the box. You do so, and you find that you've selected a $100.

What is the probability that the other bill remaining in the box you selected is also a $100?
Of necessity one box has a $1, and the other box has $100. Were no previous selections made then the chance is 50%.
And for a stranger choosing from either box the chance of getting a 1 or a 100 would be the same.
However, since this is an example of the red car problem the the chance is supposedly lower since the $1 has failed to occur twice the probabilities are not the same
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Sculptor
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Re: A fun little probability puzzle for you.

Post by Sculptor »

bobmax wrote: Sat Jul 16, 2022 9:50 am66%
No. 33%

66% chance of $1
Flannel Jesus
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Re: A fun little probability puzzle for you.

Post by Flannel Jesus »

How do you figure Sculptor?
Flannel Jesus
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Re: A fun little probability puzzle for you.

Post by Flannel Jesus »

Another way of phrasing the problem is, once you have the information that the first bill you chose was $100, what's the probability that you chose the box with 2x $100 bills?
Age
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Re: A fun little probability puzzle for you.

Post by Age »

Flannel Jesus wrote: Sat Jul 16, 2022 7:36 am Don't look up the answer or read further, try to solve it yourself first.

I present to you 4 USD bills, 1 $1 bill and 3 $100 bills. I then tell you I'm going to put 2 of these bills in one box, and the other 2 in another box - I shut a curtain and do so out of your sight. I then present you with the two boxes.

So, in front of you now are 2 boxes, both apparently identical from the outside, but one has a $1 and a $100 in it, and the other has a $100 and another $100 in it. You don't know which one is which.

Now I say, you may choose a box, so you do so - I put the other box away. I now say, reach inside and grab one of the bills inside the box. You do so, and you find that you've selected a $100.

What is the probability that the other bill remaining in the box you selected is also a $100?
Is it 50%?
Iwannaplato
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Re: A fun little probability puzzle for you.

Post by Iwannaplato »

i feel Monty Hall rolling over in his grave.
Age
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Re: A fun little probability puzzle for you.

Post by Age »

Iwannaplato wrote: Sat Jul 16, 2022 10:59 am i feel Monty Hall rolling over in his grave.
WHY?

And are you going to give your answer/guess?

If no, then WHY NOT?
Flannel Jesus
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Re: A fun little probability puzzle for you.

Post by Flannel Jesus »

What's your answer Age?
Age
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Re: A fun little probability puzzle for you.

Post by Age »

Flannel Jesus wrote: Sat Jul 16, 2022 11:32 am What's your answer Age?
The one I already gave.

What is your answer "flannel jesus"?
bobmax
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Re: A fun little probability puzzle for you.

Post by bobmax »

Sculptor wrote: Sat Jul 16, 2022 10:05 am Of necessity one box has a $1, and the other box has $100. Were no previous selections made then the chance is 50%.
And for a stranger choosing from either box the chance of getting a 1 or a 100 would be the same.
However, since this is an example of the red car problem the the chance is supposedly lower since the $1 has failed to occur twice the probabilities are not the same
Probability does not derive from things, nor from their past, but from what we now know of things.

It is what we know of the way things stand now that determines the probability of an event.

Given some knowledge, a probability arises.

But what you describe does not correspond to what is known.

And what we do know is that there are two more $ 100 and one $ 1 bills.
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Sculptor
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Re: A fun little probability puzzle for you.

Post by Sculptor »

bobmax wrote: Sat Jul 16, 2022 2:50 pm
Sculptor wrote: Sat Jul 16, 2022 10:05 am Of necessity one box has a $1, and the other box has $100. Were no previous selections made then the chance is 50%.
And for a stranger choosing from either box the chance of getting a 1 or a 100 would be the same.
However, since this is an example of the red car problem the the chance is supposedly lower since the $1 has failed to occur twice the probabilities are not the same
Probability does not derive from things, nor from their past, but from what we now know of things.

It is what we know of the way things stand now that determines the probability of an event.

Given some knowledge, a probability arises.

But what you describe does not correspond to what is known.

And what we do know is that there are two more $ 100 and one $ 1 bills.
I think you might want to read the problem again
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Sculptor
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Re: A fun little probability puzzle for you.

Post by Sculptor »

Flannel Jesus wrote: Sat Jul 16, 2022 10:21 am How do you figure Sculptor?

Because it is a version of the Monty Hall problem where having made a choice it is best to change course.
Flannel Jesus
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Re: A fun little probability puzzle for you.

Post by Flannel Jesus »

Age wrote: Sat Jul 16, 2022 1:13 pm
Flannel Jesus wrote: Sat Jul 16, 2022 11:32 am What's your answer Age?
The one I already gave.

What is your answer "flannel jesus"?
Oh my bad, didn't see that one. My answer, the canonical answer, is that there is a 2/3 chance that the remaining bill in the box you've chosen is also $100. I came to that conclusion using Bayes theorem myself
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