Two information theoreticians, X and Y, perform a trick with a shuffled deck of cards, jokers removed. X asks a member of the opposite audience to select five cards at random from the deck. The opposite audience member passes the five cards to X, who examines them, and hands one back. X then arranges the remaining four cards in some way and places them face down, in a neat pile.

Y, who has not witnessed these proceedings, then enters the room, looks at the four cards, and determines the missing fifth card, held by the audience member. How is this trick done?

Note: The only communication between X and Y is via the arrangement of the four cards. There is no encoded speech or hand signals or ESP, no bent or marked cards, no clue in the orientation of the pile of four cards...


----------------------
suresh

Hi Friends,

Try to find answer using the following hint.

HINT: In any group of five cards, at least two must be of the same suit. (This hint is designed to lead to one (particularly elegant) solution. There are other solutions to which it may not apply.)

--------------------
suresh