Notice: Home alone tonight?
The rope trick: You are a burglar at the top of a 20-meter building, which has a ledge halfway down on which it is possible to stand. There are hooks at the top of the building and on the ledge. You have a 15-meter length of rope and a knife. You can cut the rope if you like and make any type of knot anywhere on the rope, which uses up no length and which can be applied on either hook. How would you use the rope to descend the building safely? You are not allowed to jump off the building or off the rope.