500
You have a boat and need to take a fox, a chicken and some corn across a river.
The boat will only hold you and one other thing.
If you leave the chicken alone with the corn, the chicken will eat the corn.
If you leave the fox alone with the chicken, the chicken's in big trouble.
How can you get them all across in the least amount of trips possible?
First, take the chicken across and leave it there...
Go back alone...
Take the fox across...
Leave the fox and take the chicken back...
Leave the chicken and take the corn across...
Leave the corn with the fox and go back alone...
Finally, take the chicken across...