Solution to: Square and Rectangle
The picture of the rectangle is deceptive! The line XY shown in the picture of the rectangle (see below) is not a line at all. The parts XU and VY have a gradient of 2 / 5 = 0.4, and the parts XV and UY have a gradient of 3 / 8 = 0.375. In fact, XUYV is a parallelogram with an area of 1, not a line!
Two versions of this riddle are published on this site. It can also be found under: Appearing Area.