A man was travelling across the country carrying a fox, a duck, and a bag of corn, when he came to a river. There was a small boat in which he could ferry only one of the three items across the river at any one time. He could not leave the fox alone with the duck or the duck would be eaten. And he dare not leave the duck alone with the corn or the corn would be eaten. How did he get all three across?

Solution: First the man took the duck across, then he came back and took the fox over. He left the fox on the far side of the river and returned with the duck. He then left the duck on the near side and took the corn over. Then he returned and took the duck across.