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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: THERE IS NO SOLUTION! | Comment 80 of 89 |
(In reply to THERE IS NO SOLUTION! by jon)

Actually, Erik O. is anything but an "ameature".

You need to take your thinking a step further.

"if five thinks he's 5, then 5+ 17+ 7= 29, or if he assumes that he's a 7 then 7+17+7 = 31. Number 5 cannot know his number."

If five thinks he's 5, and seven sees a 5 and a 17, what will seven think?

"if seven thinks he's 7, then the 7+5+17=29, or if he assumes that hes a 19, then 19 +17+5=41. Number 7 Cannot know his number."

If seven thinks he's 7, and five sees a 7 and a 17, what will five think?

 Posted by Dustin on 2005-04-09 00:44:59

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