A man has to take a dog, a cat, and a mouse across a river. He can only take one of the animals across at a time. If he takes the mouse, the dog will eat the cat. If he takes the dog, the cat will eat the mouse.
How does he get the three animals across the river?
1. The man takes the cat across and goes back to get the mouse.
2. The man then takes the mouse across and returns with the cat.
3. The man leaves the cat on the shore and takes the dog across. He leaves the dog with the mouse.
4. The man goes back to get the cat and all of the animals have made it across the river!