A rectangular sheet of card measures 14 centimetres across and 9 centimetres from top to bottom. A rectangle 5 centimetres across and 4 centimetres from top to bottom is cut away from its top right corner, leaving an L-shape. What is the area of the L-shape?

الشرح

The uncut sheet covers 14 times 9, which comes to 126, and the corner removes 5 times 4 of those squares. Subtracting 5 plus 4 takes away only nine squares for a cut that actually swallows twenty, because it treats two edge lengths as though they were the surface between them.