This unit describes an experience in informal geometry that is based on work with construction paper and milk cartons. The description is mostly of work actually carried out by children in the elementary grades involving such mathematical concepts as congruence, symmetry, the idea of a geometric transformation, and some basic notions of elementary…

A geoboard-related extremal problem dealing with both concave and convex polygons is discussed and a proof is given of the solution. (MP)

Designs and arrangements of pentominoes are examined. (SD)

Relationships between the linear dimensions, surface area, and volume of parallelepipeds are examined. (SD)

Using the overhead projector, or overlays on an original pattern, a variety of tessellations can be generated. Several illustrations are included. (SD)

A unit on the peoperties of a kite can include many geometric concepts: symmetry, distance, relationships between diagonals, area, altitude, angles, and others. (SD)

Activities involving estimation of the number of objects in a configuration can motivate students to consider parametric models. (SD)

Having students find and cut out of graph paper the 12 pentominoes can provide an enjoyable exercise in perception, discovery, and double checking. The pentominoes can then be used to illustrate informally several geometric concepts. (SD)

Students, using the materials provided, can determine the number of diagonals, number of triangles formed by the diagonals, and degree measures of interior and exterior angles of regular polygons. The activity is designed to lead them to general formulae for polygons with n sides. (SD)

A series of lessons in which the concept of symmetry is informally developed is described. Rotational and reflection symmetries are examined. Pictures and sample worksheets illustrate the article. (SD)

A learning activity relating modular arithmetic to patterns of figures determined by points equally spaced around a circle is described. (SD)

Geometric concepts and theorems can be discovered by high school students using the materials described. Among the topics explored are Platonic solids and Euler's formula. (SD)

The use of paper folding to demonstrate polygons which give plane tessellations, conic sections, and the solutions to several problems is described. (SD)