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Finding regular polygons, such as equilateral triangles, squares, hexagons, and even octagons, in art or architecture is not unusual, but seeing a nonagon, or nine-sided regular polygon, such as the Mongolian drum (see photograph 1) is less common. Perhaps 9 is a special number in Mongolia: Shamans have 99 tengri, or spirits, (55 benevolent ones and 44 “dark” ones) on their drums, although the drums are more often circular.

### Courtney Starling and Ian Whitacre

Introduce your students to a fun and innovative game to encourage precise communication

### Maryellen Williams-Candek

Students' understanding of proportional relationships become apparent during an algebra project that focuses on constructing mathematical arguments.

### Stephan Pelikan, Anna F. DeJarnette, and Stephen Phelps

A monthly set of problems is aimed at a variety of ability levels.

### Wanda Milliman

The more connections that students can make between mathematical content and the real world, the better they will become at developing critical thinking and understanding mathematics. This lesson on exploring geometric dilations encourages small cooperative-group critiques and connections to an abundance of middle school math concepts. Graphing proportional relationships and finding the constant of proportionality are big ideas in middle school mathematics. This two-part lesson connects these ideas and many more Common Core State Standards (CCSSI 2010) through fun, student-driven activities.

### Matt B. Roscoe and Stephan Pelikan

Abstract: A monthly set of problems is aimed at a variety of ability levels.

### Joel Amidon and Matt Roscoe

A monthly set of problems is aimed at a variety of ability levels.

### Joel Amidon and Matt Roscoe

A monthly set of problems is aimed at a variety of ability levels.

### Joel Amidon and Matt Roscoe

A monthly set of problems is aimed at a variety of ability levels.