Mailman

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Two friends, Denis and Léo wish to communicate by mail.
The mailman is dishonest. He steals.
Each of the two friends has his own lock and key.
They put their mail in a secure box.

Question:
How can Denis send a letter to Léo without the mailman opening the box?

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  • 1 Answer(s)

    Denis sends a locked box with his letter to Leo.
    Leo adds his lock to the box and returns it to Denis.
    Denis gets the box, removes his lock and returns it to Leo.
    Leo can now open box safely that has his lock on it.

    pnikam Expert Answered on 17th August 2015.
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