Fox, Chicken, Corn
A farmer, a small raft, and three things that cannot be trusted with each other.
A farmer needs to get a fox, a chicken and a bag of corn across a river. The raft carries the farmer and one other thing — never two.
- Leave the fox alone with the chicken and the chicken is eaten.
- Leave the chicken alone with the corn and the corn is eaten.
- Nothing happens while the farmer is standing there.
How does he get all three across?
The trap is assuming that each thing crosses once. Work it that way and you run out of moves almost immediately — which is worth doing, because noticing which move you wish you could take is most of the answer.
- Farmer
- Fox
- Chicken
- Corn
- empty
Everything starts on this bank. The raft holds the farmer and one other thing.
If you are stuck
One question settles it: of the three, which one can be left with either of the others without incident? There is exactly one, and knowing which it is tells you what has to move first.
The other thing worth questioning is the assumption that the raft only ever comes back empty.