This number puzzle helps children develop fluency with pairs of numbers that sum to 10 while applying logic and spatial-visualization skills. Users arrange 9 small triangles within a large one so that the numbers on the matching edges total 10. Students can use the interactive Flash applet or the printable (pdf) triangles provided. The Teachers' Notes page offers suggestions for implementation, discussion questions, ideas for extension and support, and a link to related games (cataloged separately).