The picture in the puzzle looks like a simple flower, with four red petals, inside a square. But to solve the mathematical problem - finding the total area of those petals - you'll have to think outside the box and do some fast figuring. Some of these great puzzles have ancient roots, others come from Leonardo da Vinci's work; and every one's a classic. Not only will these conundrums provoke hours of thought, but the images look great too, with pictures that range from cartoon rabbits to time-lapse photography of the sky.