Once upon a time, in a small town, a merchant had the misfortune of owing a large sum of money to the moneylender. The moneylender, who was old and ugly, fancied the merchantís beautiful daughter so he proposed a bargain. He said he would forgo the merchantís debt if he could marry the daughter. Both the merchant and his daughter were horrified by the proposal.The moneylender told them that he would put a black pebble and a white pebble into an empty bag. The girl would then have to pick one pebble from the bag. If she picked the black pebble, she would become the moneylenderís wife and her fatherís debt would be forgiven. If she picked the white pebble she need not marry him and her fatherís debt would still be forgiven. But if she refused to pick a pebble, her father would be thrown into jail.
They were standing on a pebble strewn path in the merchantís garden. As they talked, the moneylender bent over to pick up two pebbles. As he picked them up, the sharp-eyed girl noticed that he had picked up two black pebbles and put them into the bag. He then asked the girl to pick her pebble from the bag.
"Oh, how clumsy of me," she said. "But never mind, if you look into the bag for the one that is left, you will be able to tell which pebble I picked." Since the remaining pebble is black, it must be assumed that she had picked the white one. And since the moneylender dared not admit his dishonesty, the girl changed what seemed an impossible situation into an advantageous one.