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# Re: [Phys-L] Inference Lab Design

• From: Jeff Bigler <jcb@mit.edu>
• Date: Sun, 19 Aug 2012 13:41:49 -0400

On 8/19/2012 2:29 AM, D.V.N. Sarma wrote:

which some of you may be knowing already.

There is a society of logicians. Anybody who wants join the society
will be given a test and only those who pass the test

Once three new candidates applied for membership. The society
devised a test for them. They were told that they will be bindfolded
and three caps will be placed one each on their heads. The caps will
be either black or white. Then their blindfolds will be removed.
The candidate cannot see the color of the cap on his own head but
only of those on the heads of the other two. A candidates who sees
one or more white caps should rise his hand. From the hands raised
one has to guess the color of the cap on his own head.

The candidates were blindfolded and three white caps were placed on
their heads. The blindfolds were removed. All the three raised hands.
Presently one of them said that his cap is white. How did he guess that?

I must be missing something. Suppose the candidate who spoke up was
candidate #3 (C3). The following situations are both possible:

C1 C2 C3
cap white white white
hand raised raised raised

C1 C2 C3
cap white white black
hand raised raised raised

--
Jeff Bigler
Lynn English HS; Lynn, MA, USA
"Magic" is what we call Science before we understand it.