This problems is an opportunity to explore triangular numbers in the familiar context of decorating a birthday cake with a number of candles corresponding to a child's age. The problem lends itself to systematic strategies and multiple representations. The Teachers' Notes page offers rationale, suggestions for implementation, discussion questions, and ideas for extension and support.

This lesson is to teach the problem-solving strategy using the CUBES acronym. The students will use digital photos to create real-life story problems of their own and practice using the CUBES strategy to solve the problems they create as well as those of their peers.