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"Search the Web to learn more about the stories behind the stamps issued by the U.S. Postal Service commemorating the people, places, events, and trends of the 1960s. Explore Web sites related to Neil Armstrong's first steps on the moon and Martin Luther King's "I Have a Dream" speech as well as the introduction of the Ford Mustang and Roger Maris's 61st home run! Included: An Internet scavenger hunt for students!"

"Search the Web to learn more about the stories behind the stamps issued by the U.S. Postal Service commemorating the people, places, events, and trends of the 1950s. Explore Web sites related to the polio vaccine, rock and roll, Brown v. the Board of Education, and I Love Lucy! Included: An Internet scavenger hunt for students!"

"A tessellation is created when a shape is repeated over and over again covering a plane without any gaps or overlaps. Another word for a tessellation is a tiling. Read more here: What is a Tiling? A dictionary* will tell you that the word "tessellate" means to form or arrange small squares in a checkered or mosaic pattern. The word "tessellate" is derived from the Ionic version of the Greek word "tesseres," which in English means "four." The first tilings were made from square tiles. A regular polygon has 3 or 4 or 5 or more sides and angles, all equal. A regular tessellation means a tessellation made up of congruent regular polygons. [Remember: Regular means that the sides and angles of the polygon are all equivalent (i.e., the polygon is both equiangular and equilateral). Congruent means that the polygons that you put together are all the same size and shape.] Only three regular polygons tessellate in the Euclidean plane: triangles, squares or hexagons. We can't show the entire plane, but imagine that these are pieces taken from planes that have been tiled. "