Counting Diagonals in a Convex Polygon Draw a convex polygon. Start connecting its vertices with non-intersecting diagonals. When you can't draw any more without intersecting existing diagonals, count their total number. See that it does not depend on the manner in which diagonals have been drawn. Fif Number from 1 through 9 are written in a row.
Players take turns selecting numbers.
The goal is to get three numbers that add up to 15. Nimble , Northcott's game , Plainim , Scoring , Turning Turtles . Every one knows this one. Solution, even if not elementary, can be explained to a preschooler. Offers a great counting exercise.