The Case of Hidden Identities

Marketing Innovation

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The Case of Hidden Identities

Marketing Innovation

A pair of sneaky spies are working together to steal a set of top-secret plans, but they have a problem: these spies always hide in the shadows, and so they do not know each other’s faces. In order to verify identities when they meet, the two spies have devised a complex scheme using simple playing cards. The first spy will choose 5 cards at random from a 52 card deck. He will look at these and choose a single card, which he keeps secret. He will then pass the other cards to the second spy in a particular order. The second spy will then look at the remaining 4 cards and must tell the first spy the suit and number of the secret card. How does the first spy choose the card to hide, and how does the second spy know which card was hidden?

Edit: The problem as stated is slightly ambiguous. To clarify: The only information that is contained in the passed cards is their ordering. All cards are passed face down, and with the same orientation!

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