From: Mark Leeds <markleeds_at_verizon.net>

Date: Tue, 26 Aug 2008 09:51:52 -0400

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 26 Aug 2008 - 13:55:56 GMT

Date: Tue, 26 Aug 2008 09:51:52 -0400

Duncan: I think I see what you're saying but the strange thing is that if
you use the utility function log(x) rather than x, then the expected values
are equal. Somehow, if you are correct and I think you are, then taking the
log , "fixes" the distribution of x which is kind of odd to me. I'm sorry to
belabor this non R related discussion and I won't say anything more about it
but I worked/talked on this with someone for about a month a few years ago
and we gave up so it's interesting for me to see this again.

Mark

-----Original Message-----

From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org] On
Behalf Of Duncan Murdoch

Sent: Tuesday, August 26, 2008 8:15 AM

To: Jim Lemon

Cc: r-help_at_r-project.org; Mario

Subject: Re: [R] Two envelopes problem

On 26/08/2008 7:54 AM, Jim Lemon wrote:

> Hi again,

*> Oops, I meant the expected value of the swap is:
**>
**> 5*0.5 + 20*0.5 = 12.5
**>
**> Too late, must get to bed.
*

But that is still wrong. You want a conditional expectation, conditional on the observed value (10 in this case). The answer depends on the distribution of the amount X, where the envelopes contain X and 2X. For example, if you knew that X was at most 5, you would know you had just observed 2X, and switching would be a bad idea.

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 26 Aug 2008 - 13:55:56 GMT

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