Linked Questions
17 questions linked to/from In the 100 blue eyes problem - why is the oracle necessary?
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In the blue-eyes puzzle, why can't they skip ahead? [duplicate]
In the solution to the Blue Eyes logic puzzle, there is a follow-up question:
Each person knows, from the beginning, that there are no less than 99 blue-eyed people on the island. How, then, is ...
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An illness at a monastery [duplicate]
In Faraway Land there is a monastery built atop a mountain in which monks live isolated from the rest of the world.
The monastery is made of two large buildings: one is where the monks sleep, the ...
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The Green-Eyed Dragons Riddle [duplicate]
You visit a remote desert island inhabited by one hundred very friendly dragons, all of whom have green eyes. They haven't seen a human for many centuries and are very excited about your visit. They ...
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How many cheating husbands? [duplicate]
There is a matriarchal town which believes that a prophetic stranger will tell the wives whether any of the husbands are cheating. The stranger will only say yes if there are any and no if there are ...
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Magical election of novices in a monastery [duplicate]
In a monastery, there is a special rite to elect new novices. All candidates (we're talking of a huge number, so let's assume an infinite amount) gather together in one hall that gets locked, so that ...
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Is it necessary to state that there is a logician with a blue hat in this 100 logicians puzzle? [duplicate]
I've been discussing the logic puzzle where 100 logicians, all wearing blue hats, are trapped in a room and told: they can leave when a bell rings if they know they know they are wearing a blue hat, ...
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Are there eighteen or twenty bars in my castle?
Two friends, Mark and Rose, are very famous logicians; they are so clever that they can deduce any logic connection possible in a matter of minutes even from the most vague situation.
Unfortunately, ...
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The Dwarves' Test
One day, the chief of the dwarves decided he wanted to test his tribe. So that night, he told the dwarves that he would paint on each dwarf's back a dot colored either red or blue. Each dwarf will ...
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Abby and Bobby and three numbers on the blackboard
Abby selects a non-negative integer $A$, and Bobby selects a
non-negative integer $B$.
They then both tell their number secretly to Summy.
Summy writes the numbers $5$, $8$, and $15$ on the ...
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10
votes
6
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Who has mud on their forehead?
This is probably my favorite puzzle. It uses logic, but it's not one of those "logic table" puzzles which i dislike immensely. What is this type of puzzle called and are there more like it ...
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Blue eyes riddle: what information is gleaned after the first night?
There are good explanations on this site and xkcd of the inductive reasoning leading to the riddle’s solution, but nowhere have I found an answer to the following aspect:
Exactly what information is ...
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The Dot-town suicide
Each resident of Dot-town carries a red or blue dot on his (or her) forehead, but if he ever figures out what color it is he kills himself. Each day the residents gather; one day a stranger comes and ...
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Blue eyes riddle: why do all nested hypotheses need to be considered?
Note: This is the second try at asking something that has not yet been answered by the excellent answers to the Oracle question or the skip-ahead question.
In this answer to my previous attempt at ...
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2
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Green Eyed Oracle Variant - Not a Multiple of $17$
$100$ perfect logicians have been gathered on an island. It is common knowledge that logicians always have blue or brown eyes, though on this island, all eyes are blue. However, there are no ...
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Variant to blue eyes puzzle - selfish logicians
This is a variation of the blue eyes puzzle.
Suppose the logicians want to get off the island. They are selfish and think only of themselves. They may help others as well, but solely for their own ...
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