A fun little probability puzzle for you.

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A fun little probability puzzle for you.

Postby Flannel Jesus » Sat Jul 16, 2022 12:45 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?
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Re: A fun little probability puzzle for you.

Postby Motor Daddy » Sat Jul 16, 2022 2:11 am

There are 4 bills total, 3 of which are 100.

That means there is only a 1 in 4 probability (25% chance) of selecting the $1 bill at the start, and a 3 in 4 probability (75% chance) of selecting a 100 dollar bill.

Since one of the $100 bills is already removed, then there is a 1 in 3 probablility of selecting the $1 bill and a 2 in 3 probablility of selecting another 100 dollar bill.

So at that point there is a 66.666...% probablilty of selecting a $100 bill, and a 33.333...% probablity of selecting a $1 bill.

That's my final answer.
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sat Jul 16, 2022 11:26 pm

You got the right answer here, Motor, numerically. So congrats on that!

This might sound silly, but I don't know if the logic you used to get there makes sense though. I assume this bit is the meat of your reasoning:

Since one of the $100 bills is already removed, then there is a 1 in 3 probablility of selecting the $1 bill and a 2 in 3 probablility of selecting another 100 dollar bill.


So I've devised an alternative scenario, to see if you can apply the same reasoning to this alternate scenario and still come to the correct conclusion.

This scenario is just like the first, but instead of 2 boxes, there are 3 boxes.
1 box has $1 and $100
1 box has $1 and $100
1 box has $100 and $100

Just like the first scenario, in this scenario you choose a box, essentially at random - you have no idea if you chose the box with 2x $100 or if you chose one of the 1 + 100 boxes. And once again, you pick out a bill at random, and you happen to find that you picked a $100.

So, just as in the first scenario, the question is, what' the probability that the other bill remaining in the box is also $100?
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 12:13 am

The probability is the same in both cases.

Because in the first you have 4 total bills spread over two boxes, and in the second you have 6 spread over 3… 2 per box in each case… and same ratio of 1s to 100s.
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Re: A fun little probability puzzle for you.

Postby Motor Daddy » Sun Jul 17, 2022 12:37 am

Flannel Jesus wrote:You got the right answer here, Motor, numerically. So congrats on that!

This might sound silly, but I don't know if the logic you used to get there makes sense though. I assume this bit is the meat of your reasoning:

Since one of the $100 bills is already removed, then there is a 1 in 3 probablility of selecting the $1 bill and a 2 in 3 probablility of selecting another 100 dollar bill.


So I've devised an alternative scenario, to see if you can apply the same reasoning to this alternate scenario and still come to the correct conclusion.

This scenario is just like the first, but instead of 2 boxes, there are 3 boxes.
1 box has $1 and $100
1 box has $1 and $100
1 box has $100 and $100

Just like the first scenario, in this scenario you choose a box, essentially at random - you have no idea if you chose the box with 2x $100 or if you chose one of the 1 + 100 boxes. And once again, you pick out a bill at random, and you happen to find that you picked a $100.

So, just as in the first scenario, the question is, what' the probability that the other bill remaining in the box is also $100?


There are 6 bills total, 4 of which are $100 bills, and 2 of which are $1 bills.
At first there is a 4 in 6 chance (66.666...%) of pulling a $100 bill, and a 2 in 6 chance (33.333...%) of pulling a $1 bill.
After picking the $100 bill out there is a 3 in 5 chance (60%) of pulling a $100 bill, and a 2 in 5 chance (40%) of pulling a $1 bill.

The boxes are a distraction, they mean nothing.

4 divided by 6 = .666... (66.666...%)
2 divided by 6 = .333... (33.333...%)

3 divided by 5 = .60 (60%)
2 divided by 5 = .40 (40%)
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 12:58 am

Would you say the same thing about the boxes being a distraction if a 1 had been drawn?
Fall semester ends 12/16/22. Apologies if I do not reply immediately.

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Re: A fun little probability puzzle for you.

Postby Motor Daddy » Sun Jul 17, 2022 1:47 am

Ichthus77 wrote:Would you say the same thing about the boxes being a distraction if a 1 had been drawn?


If there were 6 bills at the start, 4 being $100 and 2 being $1, then after drawing a $1 there would be 4 $100 and 1 $1 remaining.

So the percentages would be 4 in 5 (80%) for $100 bills, and 1 in 5 (20%) for $1 bills.

Put 17 marbles in a hat, of which 16 are red and 1 is blue. There is a 1 in 17 chance (5.88%) of you picking the blue marble and a 16 in 17 chance (94.11%) of picking a red marble.

If there are 6 numbers, each between 1 and 50, then there are 50 x 50 x 50 x 50 x 50 x 50 (15,625,000,000) possible combinations. If you buy one ticket with one combination of numbers you have a 1 in 15,625,000,000 chance (.0000000064%) of winning. If you have two sets of numbers you have a 2 in 15,625,000,000 chance of winning. In order to have a 100% probability you would need to buy 15,625,000,000 tickets with every different combination of numbers, and you would be in debt after winning, from buying all those tickets, even if you won a billion dollars!. :) At $1 per set of numbers you would have paid 15.6 BILLION dollars to win 1 billion LOL. It's not economically feasible. :)

Ever buy a lottery ticket and look at the odds of winning?
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 2:22 am

You’re not answering my question.

Kinda answers my question.

P.s. I bought two lottery tickets in my life. Once when I turned the legal age to buy a lottery ticket. Once when I was delusional. Someone always wins. Eventually.
Fall semester ends 12/16/22. Apologies if I do not reply immediately.

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Re: A fun little probability puzzle for you.

Postby Motor Daddy » Sun Jul 17, 2022 2:24 am

Ichthus77 wrote:You’re not answering my question.


Did I mention a box? There's your answer!
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 2:30 am

You have 100% chance of drawing a $100 after a $1. The boxes are not a distraction.

It’s like my dad just let me win at chess. *eyeroll* ;)
Fall semester ends 12/16/22. Apologies if I do not reply immediately.

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- A marriage of Sartre & Levinas

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Re: A fun little probability puzzle for you.

Postby Motor Daddy » Sun Jul 17, 2022 2:48 am

Ichthus77 wrote:You have 100% chance of drawing a $100 after a $1. The boxes are not a distraction.

It’s like my dad just let me win at chess. *eyeroll* ;)


How could you possibly have a 100% chance of drawing $100 after $1, when there is still a $1 left to be drawn??

The boxes are a distraction.
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 3:28 am

Really? You found a box with a 100% chance of drawing $100 & you’re going to, what, take your chances with another box? Those other two boxes are a distraction, yes, but that first box… not a distraction.
Fall semester ends 12/16/22. Apologies if I do not reply immediately.

“In choosing myself, I choose the other.”
- A marriage of Sartre & Levinas

“ Gloria Dei est vivens homo. “
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- Irenaeus
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 8:38 am

Ichthus77 wrote:The probability is the same in both cases.

Because in the first you have 4 total bills spread over two boxes, and in the second you have 6 spread over 3… 2 per box in each case… and same ratio of 1s to 100s.

Not the same ratio of 1s to 100s
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 8:41 am

Motor Daddy wrote:The boxes are a distraction, they mean nothing.

4 divided by 6 = .666... (66.666...%)
2 divided by 6 = .333... (33.333...%)

3 divided by 5 = .60 (60%)
2 divided by 5 = .40 (40%)

The boxes are not just a distraction, they mean something. I'm glad I asked the second scenario, because my intuition was right, I see the logic you're using and it's not generalisable to other scenarios.

The probability of pulling another 100 out of the same box in the second scenario is 1/2
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Re: A fun little probability puzzle for you.

Postby Ichthus77 » Sun Jul 17, 2022 9:06 am

Flannel Jesus wrote:
Ichthus77 wrote:The probability is the same in both cases.

Because in the first you have 4 total bills spread over two boxes, and in the second you have 6 spread over 3… 2 per box in each case… and same ratio of 1s to 100s.

Not the same ratio of 1s to 100s


I think you’re confused how I figured the ratio. Whenever there is a 1, there is a 100. In the first scenario, that happens 1/2 boxes. In second scenario, that happens 2/3 boxes. Do it again… 3/4 boxes. And so on.

In scenario 1, one $1, three $100s. 4 bills. 2 boxes.
Box 1: $1, $100
Box 2: $100, $100

In scenario 2: two $1s, four $100s. 6 bills. 3 boxes.
Box 1: $1, $100
Box 2: $1, $100
Box 3: $100, $100

That there are 4 bills over 2 boxes, and 6 bills over 3 boxes, two in each box… I don’t know how to explain or say it to you, but the proportion of 1s and 100s is balanced between the scenarios. If you did 8 bills over 4 boxes, you’d have three 1s and five 100s. Balanced the same as the first two scenarios.
Box 1: 1, 100
Box 2: 1, 100
Box 3: 1, 100
Box 4: 100, 100
Fall semester ends 12/16/22. Apologies if I do not reply immediately.

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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 9:15 am

The ratio is literally not the same. Neither before you select the firt $100, nor after.

In the first scenario, before you select the $100 out of the box, you have
1x $1
3x $100
1:3

In the second scenario, before you select the $100, you have
2x $1
4x $100
2:4

So in the first scenario, you have 3 times as many 100s. In the second scenario, you have twice as many 100s.

But you're not being very clear or specific in your wording, so I'll give you the benefit of the doubt and assume that MAYBE you meant after you select the $100, the ratios are the same, so let's look at that scenario:

In the first scenario, after you select the $100 out of the box, you have
1x $1
2x $100
1:2

In the second scenario, after you select the $100, you have
2x $1
3x $100
2:3

So looking at "after" also does not give you the same ratio of 1s to 100s.

You're right, I am very confused about how you figured out the ratio.
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Re: A fun little probability puzzle for you.

Postby obsrvr524 » Sun Jul 17, 2022 10:18 am

Flannel Jesus wrote:The probability of pulling another 100 out of the same box in the second scenario is 1/2

You lost me with that one. :lol:
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 10:24 am

Ichthus77, the ratio of bills to boxes is the same: there are always twice as many bills as boxes (because we put two bills in each box) but it doesn't sound like that's what you're saying.

There's is a consistent patterned relationship between the number of 1s and the number of 100s, but that consistent relationship is not "the ratio is always the same". The relationship is, there's always 2 more 100s than there's are 1s
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 10:27 am

obsrvr524 wrote:
Flannel Jesus wrote:The probability of pulling another 100 out of the same box in the second scenario is 1/2

You lost me with that one. :lol:

I could prove it in two ways, experimentally with code, or using Bayes theorem. Choose your poison

But in simple terms, there are two ways that you could have chosen a box with $1 and $100, and also two ways you could have chosen the box with 2x $100.

That above logic works for the first example too, there are two ways you could have chosen 100 from the 2x 100 box but only one way from the other box, hence the 2/3 probability

How would you solve the problem?
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Re: A fun little probability puzzle for you.

Postby obsrvr524 » Sun Jul 17, 2022 10:55 am

Flannel Jesus wrote:How would you solve the problem?

Before we get into the truth - I would like to get a clear picture of your argument. :D

Flannel Jesus wrote:But in simple terms,
  • there are two ways that you could have chosen a box with $1 and $100, and
  • also two ways you could have chosen the box with 2x $100.

Could you explain the "two ways" for both of those?
              You have been observed.
    Though often tempted to encourage a dog to distinguish color I refuse to argue with him about it
    It's just the same Satanism as always -
    • separate the bottom from the top,
    • the left from the right,
    • the light from the dark, and
    • blame each for the sins of the other
    • - until they beg you to take charge.
    • -- but "you" have been observed --

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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 10:58 am

I don't feel 100% comfortable with this wording, but it seems to consistently match the results that I get using Bayes theorem so I'll go with it:

You need to treat each $100 bill separately. So you could have chosen the box with 2x100 and chosen the first 100 bill, or you could have chosen the box with 2x100 and chosen the second 100 bill
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Re: A fun little probability puzzle for you.

Postby MagsJ » Sun Jul 17, 2022 11:02 am

Flannel Jesus wrote:You need to treat each $100 bill separately. So you could have chosen the box with 2x100 and chosen the first 100 bill, or you could have chosen the box with 2x100 and chosen the second 100 bill

:shock:

May I ask what strand of maths this inquiry, is in? if you do not mind me asking.
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Re: A fun little probability puzzle for you.

Postby Flannel Jesus » Sun Jul 17, 2022 11:08 am

Probabilities, statistics
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Re: A fun little probability puzzle for you.

Postby obsrvr524 » Sun Jul 17, 2022 11:15 am

Flannel Jesus wrote:I don't feel 100% comfortable with this wording, but it seems to consistently match the results that I get using Bayes theorem so I'll go with it:

You need to treat each $100 bill separately. So you could have chosen the box with 2x100 and chosen the first 100 bill, or you could have chosen the box with 2x100 and chosen the second 100 bill

So you are saying that if you got a $100 - there are two ways that could have happened -
  • Chose a $100 and $100
    -- (1:3 probability of getting that box followed by 1:2 of getting that bill
    -- 1/3 * 1/2 = 1/6 for bill(#1)
  • Chose a $100 and $100
    -- (1:3 probability of getting that box followed by 1:2 of getting that bill
    -- 1/3 * 1/2 = 1/6 for that bill(#2)

So you conclude -- ?
              You have been observed.
    Though often tempted to encourage a dog to distinguish color I refuse to argue with him about it
    It's just the same Satanism as always -
    • separate the bottom from the top,
    • the left from the right,
    • the light from the dark, and
    • blame each for the sins of the other
    • - until they beg you to take charge.
    • -- but "you" have been observed --

The prospect of death weighs naught upon the purpose of life - James S Saint - 2009
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Re: A fun little probability puzzle for you.

Postby MagsJ » Sun Jul 17, 2022 11:22 am

Flannel Jesus wrote:Probabilities, statistics

I meant what theorem/s specifically, to calculate this/a/any probability?
The possibility of anything we can imagine existing is endless and infinite.. ~MagsJ

I haven't got the time to spend the time reading something that is telling me nothing, as I will never be able to get back that time, and I may need it for something important at some point in time.. Huh!? ~MagsJ

You’re suggestions and I just simply don’t mix.. like oil on water, or a very bad DJ ~MagsJ

Examine what is said, not him who speaks ~Arab proverb

aes Sanātana Dharma Pali: the eternal way ~it should not be rigid, but inclusive of the best of all knowledge for the sake of Ṛta.. which is endless.
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