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This problem isn't remotely unique to Khan, but I'm a bit put off by the "Learn the Skill" call. That said, here are my potential additions: 1) What are the lengths of the hypotenuses? (easy) 2) How many triangles until the hypotenuse length exceeds 5 units? 3) How many triangles until the SUM of hypotenuse lengths exceeds 5 units? (never done this. How would a MS or geometry student attempt?) 4) How many triangles until the figure begins to overlap itself? (never done. How would a MS student attempt?) There must be many other GREAT problems here. Thoughts?