The birthday cake is square. It has icing all over the top and down all four rectangular sides.
The top of the cake is 20cm by 20cm.
How should the cake be cut so that everyone has an equal share of the icing?
Mark the perimeter of the square at 4cm intervals. Join each mark to the centre of the top of the cake. Cut vertically downwards along the lines formed. Each person then gets a triangular piece of icing from the top of the cake and a rectangular piece of icing from the side. The rectangular pieces are identical in shape. The triangular pieces are not the same shape but they all have the same area.