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 Prime Perimeter (Posted on 2005-03-11)

You and two other people have numbers written on your foreheads. You are all told that the three numbers are primes and that they form the sides of a triangle with a prime perimeter. You see 5 and 7 on the other two heads and both of the other people agree that they cannot deduce the number on their own foreheads.

 See The Solution Submitted by Erik O. Rating: 2.8235 (17 votes)

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 re: A solution to Pat | Comment 74 of 89 |
(In reply to A solution by Pat Whitaker)

Pat, you wote :

"If I had an 11 then then the fellow with the 7 would see 5 and 11.  leaving only the choices of 3 or 7 for his number. Since the triangle 3,5,11 is impossible 7's owner would be able to determine his own number."

I stopped  to read your solution at this point, because the fellow with the 7, seeing 5 and 11, could have a 13 (that is prime) and 5 + 11 + 13 = 29, also a prime (perimeter), so, he is in doubt if he has a 7 or a 13.

 Posted by pcbouhid on 2005-04-05 16:07:25

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