A maiden must draw one of two pebbles from a bag, said to be one white and one black, to win her freedom...

logic/two.black.pebbles New

New entry, edited from material collected for the archive and not yet in a released version.

Problem

A maiden must draw one of two pebbles from a bag, said to be one white
and one black, to win her freedom with the white; the bag secretly
holds two black pebbles.  How can she win?

        A beautiful young lady is betrothed to a mean old merchant
        but she loves a young shepherd.

        When she and the shepherd confront the merchant and ask if he
        will forfeit her, the merchant takes them down to a rocky beach
        strewn with black and white pebbles.

        He picks up two pebbles and places them in a bag, then he
        turns around to face the young girl and tells her that in
        the bag are one white pebble and one black pebble.

        She must place her hand in the bag and draw one of the two
        pebbles.  If she draws the white one she will be freed from her
        betrothal and can go and marry the shepherd.
        But if she draws the black one then she will be forced to marry
        the merchant and the shepherd will be taken out to sea and fed to
        the sharks !

        Unbeknownst to our fair maiden the merchant has placed TWO
        BLACK PEBBLES in the bag !

        She doesn't trust the merchant but is forced to do as he says
        for should she refuse, the merchant would have them both arrested
        and hanged as was the customary punishment betraying ones
        betrothed.

        How can she possibly win ?

-- Giovanni Poeti <050gio@cosmos.wits.ac.za>, August 1994

[ Editor: the first paragraph is the editor's summary. ]

Show solution

Take out a pebble and dispose of it without allowing anyone to see the
colour thereof.  Then the merchant must take the other pebble out of
the bag to show what colour pebble the maiden had taken out.

C'est tout.

-- Roelof J. van Suilichem <rvsuilic@ksi.co.za>