NOTE: Grid Grouping: Part 3 adds an additional element that makes if significantly more difficult than parts 1 and 2. I would suggest using these activities in order.
I currently teach remedial 6th, 7th, and 8th graders who have not met the state standard in math. This is a discovery activity so the students have freedom to solve this problem in any manner they see fit. The angled lines give me great information as to whether or not my students understand how to use triangle for area as well.
This activity is one of many parts of my Grid Grouping set. This set has propelled my students into using area of squares, rectangles, and right triangles through discovery and has also led them towards percent applications.