[extropy-chat] three coins in a fountain

Eliezer S. Yudkowsky sentience at pobox.com
Fri Oct 21 19:27:43 UTC 2005

Brandon Reinhart wrote:
>>What is the probability that the other side is a tail?
> This sounds like a problem for Bayes Theorem.


> The likelihood that the coin drawn has a tail on the other side is 50%. In
> fact, the information we are given (that we see a head) doesn't help us at
> all. It is completely irrelevant information (as far as probability is
> concerned).

Sorry, no.  If a double-headed coin is drawn, it is twice as likely to 
make us see a head as an ordinary coin.  That affects the prior odds.

You may want to read this:

Eliezer S. Yudkowsky                          http://singinst.org/
Research Fellow, Singularity Institute for Artificial Intelligence

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