The landowner in the illustration is consulting with his bailiff over a
rather puzzling little question. He has a large plan of one of his
fields, in which there are eleven trees. Now, he wants to divide the
field into just eleven enclosures by means of straight fences, so that
every enclosure shall contain one tree as a shelter for his cattle. How
is he to do it with as few fences as possible? Take your pencil and draw
straight lines across the field until you have marked off the eleven
enclosures (and no more), and then see how many fences you require. Of
course the fences may cross one another.