A bee keeper needs to cross a river to collect honey from his bee hives. The only way to cross the river is in a little boat. To complicate matters, the bee keeper is being accompanied by a mouse, a cat and a dog. He can only fit one of these in the boat with him at any one time. Unfortunately, the dog cannot be left alone with the cat, and the cat cannot be left alone with the mouse.
How can the bee keeper get to his bee hives with all three of the animals?
[Answer] The bee keeper must first cross the river with the cat (so as not to leave the dog and cat, or cat and mouse unaccompanied together). Upon reaching the other side of the river, the bee keeper can return alone and pick up the mouse. Once the mouse has been taken across the river, the bee keeper must return with the cat (so as not to leave the mouse with the cat) and take the dog across. The bee keeper then return one final time to collect the cat.