The mouse, the elephant, the dog, and the cat
Just to illustrate how exactly the same puzzle can be presented in a different setting, here is the above puzzle dressed up differently.
A circus owner wants to transport his elephant, his dog, his cat and his mouse across a river. He can take one at a time across the river. But, unless he is there, the cat will fight with the mouse, the dog will fight with the cat, and the elephant will fight with the dog. However, as everyone knows, the elephant is frightened of the mouse, and if the mouse is present, the elephant will not fight with the dog.
By taking the animals back and forth, how does the circus owner get all across without any fighting breaking out?
For yet another variation and a nice discussion of it, see The lettuce-fearing leviathan in the book A fine math you've got me into by Ian Stewart.
A circus owner wants to transport his elephant, his dog, his cat and his mouse across a river. He can take one at a time across the river. But, unless he is there, the cat will fight with the mouse, the dog will fight with the cat, and the elephant will fight with the dog. However, as everyone knows, the elephant is frightened of the mouse, and if the mouse is present, the elephant will not fight with the dog.
By taking the animals back and forth, how does the circus owner get all across without any fighting breaking out?
For yet another variation and a nice discussion of it, see The lettuce-fearing leviathan in the book A fine math you've got me into by Ian Stewart.