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        riddles >> medium >> 7 stamps
        
(Message started by: Altamira_64 on Feb 2^nd, 2013, 6:25am)

Title: 7 stamps
Post by Altamira_64 on Feb 2^nd, 2013, 6:25am

Three perfct logicians were shown 7 stamps: two red, two yellow and three green. They were then blindfolded and a stamp was pasted to each of their foreheads and the remaining stamps were hidden in a drawer. When the blindfolds were removed, A was asked, "Do you know one color that you definitely do not have?" A replied, "No." Then B was asked the same question and replied, "No."
Is it possible, from this information, to deduce the color of A's stamp? Or B's stamp? Or C's stamp? If so, which one(s) and what is(are) the color(s)? (And why.) If not, why not?

Title: Re: 7 stamps
Post by SMQ on Feb 2^nd, 2013, 7:14am

We know only that [hide]C has a green stamp.[/hide]
A's "no" implies [hide]B and C do not both have red or yellow.[/hide]
B's "no" further implies [hide]C does not have red or yellow (or else, B would know their own stamp could not match C's) Therefore C's stamp is green.[/hide]
Beyond that [hide]nothing is known about the color of A's or B's stamps; all 9 possibilities are consistent with the two given statements.[/hide]

--SMQ