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There are 3 paper plates, in which A is written on one, B on the 2nd, and C on the third. Now the person performing the trick knows the initial order of the paper plates. He then asks an audience volunteer to choose one of the plate letters and commit it to memory without telling the performer. Now the plates get turned over, so the letters can't be seen. The performer then turns around and asks the volunteer to switch the two plates that he DIDN'T choose around only once. Meaning: If the volunteer chose A, switch the positions of B and C. Now the performer turns back around and asks the volunteer to switch the 3 plates around as many times as he want, but he's allowed to watch (the plates are still turned upside down). After the volunteer is content with switching the paper plates as many times as he want, the performer then flips each plate over. He then is able to somehow guess the correct plate that the volunteer committed to memory! Now here are some hints:

  1. When the performer is turned around, and you cheat and switch the plate that you actually DID commit to memory, or you switch multiple times, he isn't able to guess the correct plate at end.

  2. Since the plates are upside down after the volunteer switches the two plates, the significance behind it doesn't make sense (because the performer ONLY knows initial order of plate, and final), but obviously it is significant based on #1.

  3. Now, apparently, the first plate he flips over is meaningful and and he always flips the leftmost or bottom-most plate.

  4. The method/trick behind this is supposed to be super simple.

I apologize, I forgot to add that marking of the plates isn't possible, as the volunteer is the one who writes the letters, and the performer also said that he doesn't look for any bends in the paper plate or anything.

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up vote 2 down vote accepted

the magician stores in his memory the initial positions of the plates. then the person does one switch and magician knows the plate chosen by him is the only one in the 'right' position. the next switches don't matter because the magician sees them so he knows which plate should be where (if the person didn't do his first secret switch). he then turns the plates over and the only plate in the 'right' position (the position in which it would be without the secret swtich) is the one chosen initially

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It suffices just to follow one plate, say in the initial A position. If it is still A then A was chosen. If it is B then C was chosen. If it is C then B was chosen. – WimC Jun 22 '14 at 14:35
But the volunteer is allowed to move the plates around as many times as possible after the first switch (when the performer is turned around), so most of the times, the chosen plate isn't even in the initial place. – USER1234567890 Jun 22 '14 at 14:39
WimC you're right, that's nice. @USER1234567890 - these switches don't matter - the magician sees them so he can note what is being done and then just reverse this process to come back to the state after the first switch (he can just do it mentally, no need to actually move the plates). to understand that just imagine that there were no 'secret' switches. someone is just switching the plates around on my eyes - surely I know exactly what he did as long as my memory is sufficiently good to keep track of it – mm-aops Jun 22 '14 at 14:46

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