POST AND RAIL PUZZLE
Put the following question to the company: Supposing there was a tunnel through a hill and a post and rail fence was constructed through it, and another fence was made exactly above it, over the hill, how many more posts would be required for the latter route, supposing they were the same distance apart by both routes?
After several calculations have been made you can astonish the company by telling them that exactly the same number of posts would be required for both routes, which you can prove by making a rough sketch of the diagram, [Fig. 25], and placing matches on it to represent the posts.
Fig. 25.