This link, Area Formulas, will take you to a page where the area formulas are derived for the rectangle, square, paralelogram, triangle ,and trapezoid. These are short videos, no longer than 4 minutes, where an instructor uses grid paper and paper models.
Click on this link, here, to find an online source for printing various types of graph paper in pdf format.
Click on this link, here, to find an online source for printing various types of graph paper in pdf format.
Click here, to play KenKen puzzles.