Rectangular Cake Puzzle

Rectangular Cake Puzzle

Given a rectangular cake with a rectangular piece removed.

How can you cut the rectangle in two equal parts with one straight line cut of a knife? (The cut is of any size and any orientation, the removed piece can be one of the layers of the cake)

Solution : 

We can cut the cake by the line joining the center of the original cake and the center of the removed piece, which will divide the rectangular cake into exactly two pieces.

As the image depicts,

Area of the upper portion = m1 – n1

Area of the lower portion = m2 – n2

Now as m1 = m2 & n1 = n2 , thus Area of the upper portion = Area of the lower portion.