You have a chicken, a fox, and a bag of seed to bring across a river in a basket. The basket can only hold you to move it and one item. If you leave the chicken alone with the feed, the chicken will eat the feed. If you leave the chicken alone with the fox, the fox will eat the chicken! How do you bring all three across safely?
Keep in mind you can always bring an item back across.
Take the chicken first, then go back and get the feed and take the chicken back. Then take the fox, and the chicken again.