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con771
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 Posted: Wed Jun 25, 2008 1:11 pm Post subject: Probability Question |
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| If there are 2 choices (doors) and 20 people choose either door 1 or door 2. What is the probability that 2 people will choose door 1 and 18 people will choose door 2. I have struggled with this for sometime now. I thought it would be simply (1/2)^20 but I am not so sure. Any Help |
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The Qurqirish Dragon
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| Posted: Wed Jun 25, 2008 1:43 pm Post subject: Re: Probability Question |
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On Jun 25, 9:11 am, con771 <k...@gw-consultants.com> wrote:
| Quote: |
If there are 2 choices (doors) and 20 people choose either door 1 or door 2. What is the probability that 2 people will choose door 1 and 18 people will choose door 2. I have struggled with this for sometime now. I thought it would be simply (1/2)^20 but I am not so sure. Any Help
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Assuming everyone is equally likely to choose either door, then the
probability of a SPECIFIC two to choose door 1, and the others to
choose 18 is (1/2)^20. Now, you simply need to find how many ways you
can choose 2 out of the 20 people to be those specific people. |
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The World Wide Wade
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| Posted: Thu Jun 26, 2008 5:18 am Post subject: Re: Probability Question |
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In article
<29628776.1214399521380.JavaMail.jakarta@nitrogen.mathforum.org>,
con771 <ken@gw-consultants.com> wrote:
| Quote: |
If there are 2 choices (doors) and 20 people choose either door 1 or door 2.
What is the probability that 2 people will choose door 1 and 18 people will
choose door 2. I have struggled with this for sometime now. I thought it
would be simply (1/2)^20 but I am not so sure. Any Help
|
It's the same as the probability that a binary sequence of length 20
has two 0's and 18 1's. You can see that (1/2)^20 is not the answer
because both 1 1 0 0 ... 0 and 0 0 ... 0 1 1 qualify, and each has
probability (1/2)^20, so you're already up to 2*(1/2)^20 just looking
at these twwo. |
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David C. Ullrich
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| Posted: Thu Jun 26, 2008 11:00 am Post subject: Re: Probability Question |
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On Wed, 25 Jun 2008 06:43:30 -0700 (PDT), The Qurqirish Dragon
<qurqirishd@aol.com> wrote:
| Quote: |
On Jun 25, 9:11 am, con771 <k...@gw-consultants.com> wrote:
If there are 2 choices (doors) and 20 people choose either door 1 or door 2. What is the probability that 2 people will choose door 1 and 18 people will choose door 2. I have struggled with this for sometime now. I thought it would be simply (1/2)^20 but I am not so sure. Any Help
Assuming everyone is equally likely to choose either door, then the
probability of a SPECIFIC two to choose door 1, and the others to
choose 18 is (1/2)^20. Now, you simply need to find how many ways you
can choose 2 out of the 20 people to be those specific people.
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Hmm. "choose 2 out of 20"... nope, doesn't ring any bells.
David C. Ullrich
"Understanding Godel isn't about following his formal proof.
That would make a mockery of everything Godel was up to."
(John Jones, "My talk about Godel to the post-grads."
in sci.logic.) |
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con771
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| Posted: Thu Jun 26, 2008 11:34 am Post subject: Re: Probability Question |
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| So can someone please help me with the answer? Thanks |
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The Qurqirish Dragon
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| Posted: Thu Jun 26, 2008 1:50 pm Post subject: Re: Probability Question |
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On Jun 26, 3:58 am, David C. Ullrich <dullr...@sprynet.com> wrote:
| Quote: |
On Wed, 25 Jun 2008 06:43:30 -0700 (PDT), The Qurqirish Dragon
qurqiri...@aol.com> wrote:
On Jun 25, 9:11 am, con771 <k...@gw-consultants.com> wrote:
If there are 2 choices (doors) and 20 people choose either door 1 or door 2. What is the probability that 2 people will choose door 1 and 18 people will choose door 2. I have struggled with this for sometime now. I thought it would be simply (1/2)^20 but I am not so sure. Any Help
Assuming everyone is equally likely to choose either door, then the
probability of a SPECIFIC two to choose door 1, and the others to
choose 18 is (1/2)^20. Now, you simply need to find how many ways you
can choose 2 out of the 20 people to be those specific people.
Hmm. "choose 2 out of 20"... nope, doesn't ring any bells.
Too obvious?  |
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[Mr.] Lynn Kurtz
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| Posted: Thu Jun 26, 2008 9:11 pm Post subject: Re: Probability Question |
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On Thu, 26 Jun 2008 07:34:00 EDT, con771 <ken@gw-consultants.com>
wrote:
| Quote: |
So can someone please help me with the answer? Thanks
|
What is it about the Dragon's reply:
"Assuming everyone is equally likely to choose either door, then the
probability of a SPECIFIC two to choose door 1, and the others to
choose 18 is (1/2)^20. Now, you simply need to find how many ways you
can choose 2 out of the 20 people to be those specific people."
that you don't understand?
Additional hint: If X = number of people choosing door 1 has a
binomial distribution (does it?) with n = 20 and p = 1/2, what is the
probability that X = 2?
--Lynn |
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The World Wide Wade
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| Posted: Thu Jun 26, 2008 10:53 pm Post subject: Re: Probability Question |
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In article
<6713705.1214480071077.JavaMail.jakarta@nitrogen.mathforum.org>,
con771 <ken@gw-consultants.com> wrote:
| Quote: |
So can someone please help me with the answer? Thanks
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We already did. You're supposed to do something too. |
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