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http://math.stackexchange.com/questions/371184/predicting-real-numbers
Predicting Real Numbers edited May 15 '13 Jared Mathematics Stack Exchange
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Here is an astounding riddle that at first seems impossible to solve. I'm certain the axiom of choice is required in any solution, and I have an outline of one possible solution, but would like to see how others might think about it.

100 rooms each contain countably many boxes labeled with the natural numbers. Inside of each box is a real number. For any natural number n, all 100 boxes labeled n (one in each room) contain the same real number.
In other words, the 100 rooms are identical with respect to the boxes and real numbers.

Knowing the rooms are identical, 100 mathematicians play a game. After a time for discussing strategy, the mathematicians will simultaneously be sent to different rooms, not to communicate with one another again.
While in the rooms, each mathematician may open up boxes (perhaps countably many) to see the real numbers contained within.
Then each mathematician must guess the real number that is contained in a particular unopened box of his choosing.
Notice this requires that each leaves at least one box unopened.

99 out of 100 mathematicians must correctly guess their real number for them to (collectively) win the game.
What is a winning strategy?
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