Point E lies on segment AB, and point C lies on segment FG.
The area of parallelogram ABCD is 20 square units.
What’s the area of parallelogram EFGD?

Source: Alfred S. Posamentier, Math Wonders to Inspire Teachers and Students, 2003.)

The parallelogram can be skewed without changing its area.  Slide FG along the line containing it so that G coincides with C.  EFGD now has the same base and height with ABCD.  So the areas are the same: 20.

Posted by Jer on 2017-08-01 10:55:04