Subject:
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Re: math question (or pattern... whatever...)
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Newsgroups:
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lugnet.off-topic.geek
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Date:
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Mon, 3 Mar 2003 22:18:01 GMT
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Viewed:
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292 times
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In lugnet.off-topic.geek, Dave Schuler writes:
> In lugnet.off-topic.geek, David Koudys writes:
>
> > Here's [my friend's] rationale, hopefully explained more fully (but I still
> > think it's not quite kosher...)
> >
> > The time of the event--you grabbed 2 marbles
> >
> > there are 6 possible combinations in your hand
> >
> > r(1) r(2)
> > r(1) b
> > r(1) w
> > r(2) b
> > r(2) w
> > b w
> >
> > those are the 6 unique possibilities in your hand at the time of the event
> >
> > One of those possibilities becomes invalidated because as soon as we see one
> > of the marbles, we know it's red so the b w is gone...
> >
> > thus leaving only 5 possibilities, and what we want is the chance that both
> > marbles are red, from the event--
> >
> > 1 in 5, = 20 percent.
> >
> > I understand it, but it still isn't sitting right with me.
>
> Hmm... I just thought of something. Are there two separate questions at
> work here?
>
> Question 1: Having drawn two marbles from a bag of two red, one white, and
> one blue marbles, what are the odds that the two you have drawn are both red?
>
> Question 2: Having verified that one of the two marbles is red, what are
> the odds that the second marble is also red?
>
> Or is Q2 subordinate to Q1?
>
> Darn it, I wish I'd paid more attention in statistics, lo these many years ago.
>
> Dave!
The original question:
4 marbles in a bag, 2 are red, one is white, one is blue
You reach into the bag and grab 2 of them.
You see that one of the marbles in your hand is red.
What is the chance (either fraction or percent) that the other marble in
your hand is also red?
That's the question.
My original answer was 1 in 3, or 33 percent.
And that hasn't changed (yet)
My friend is still adamant about the 1 in 5, or 20 percent.
And I thank you for all the answers thus far, it helps me to formulate a
concise, clear response.
Dave K
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Message is in Reply To:
 | | Re: math question (or pattern... whatever...)
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| (...) Hmm... I just thought of something. Are there two separate questions at work here? Question 1: Having drawn two marbles from a bag of two red, one white, and one blue marbles, what are the odds that the two you have drawn are both red? (...) (22 years ago, 3-Mar-03, to lugnet.off-topic.geek)
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