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Magic trick (Posted on 2007-05-11) Difficulty: 3 of 5
Two magicians A and B perform the following trick:

A leaves the room and B chooses 4 members from the audience at random. Each member chooses a card numbered from 1 to 100 (each chooses a different card) and after B has seen their cards he chooses a card from the remaining deck of cards. The 5 chosen cards are shuffled by an audience member and handed to A who just returned to the room. Prove that A is able to figure out which cards each member picked. Consider that the chosen members form a row and e.g. the leftmost member picks the first card and the rightmost member (B) picks the last card.

No Solution Yet Submitted by atheron    
Rating: 4.1667 (6 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
A Little Hocus Pocus | Comment 12 of 51 |
I have refrained from entering this debate because although I can perform this trick I cannot reveal the method. (It was taught to me by a Magic Circle Member with that condition)
I make the following points.
Determining the "odd card out" - the one selected by B is simple requiring a little memory and simple calculation.
Determining the order is harder. It is easy if you use a "tell" or trick. ie how you stand; what you say - "Can you tell me the card"; "Name the card". etc.
To do it with "pure calculation" would require a  very clever calculator (able to do complex multiplication and division; or determine roots; mentally) These people do exist but are exceptional.

  Posted by Vernon Lewis on 2007-05-12 10:49:14
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