Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.


Math Forum
»
Discussions
»
sci.math.*
»
sci.math
Notice: We are no longer accepting new posts, but the forums will continue to be readable.
Topic:
Brainteaser n
Replies:
15
Last Post:
Aug 6, 2003 7:10 AM




Re: Brainteaser n
Posted:
Jan 13, 2003 11:39 PM


For those who are interested, here is a brainteaser that took me more than 15 mins to solve (apologies to those who don't think it belongs here, and to the person I pinched it from)
On the Isle of Reason live exactly 50 logicians. There are no other inhabitants. Each day they all meet to discuss riddles and life. However there is one topic they do not discuss. On each of their foreheads is a blue dot. However it is so shameful to have a blue dot, that knowing this fact for a certainty, will certainly result in the bearers' suicide the next morning. For this reason blue dots and related things are NEVER discussed. Fortunately there are no mirrors or reflections on the island and so everyone is blissfully unaware of the blue dot they have, but can see the other 49 blue dots....until, one day a visitor to the island comes and knowing something of the strange problems of the island thinks he will be tactful and announces "I happen to have noticed that at least one of you has a blue dot on his forehead". He leaves the island unaware of what follows. Precisely fifty nights pass and on the next morning all fifty logicians commit suicide. Why?
Note: there is sufficient information in the riddle, it is not a play on words and can be solved by pure logic. The fact that they discuss riddles is irrelevant. They could come together each day without a word being spoken!
Finally, for those who have heard the riddle, answer this. Why does someone need to come to the island and say that there is a blue dot? Surely each of them can see 49 other dots and knows that there is a blue dot? The answer must be as tight as the answer to the riddle!
Bill.



