# Cross Number Puzzles: Arithmetic to algebra

Cross number puzzles are elementary-school-sized spreadsheets. They are introduced in K as a chart-form for sorting objects by two attributes. The very same logical structure is later used to develop the addition and subtraction algorithms, and to explain and develop the multiplication and division algorithms.

Two PowerPoints are available for professional development.

- The first shows how the Cross Number Puzzle format provides a common structure for essential mathematical ideas across the grades.
- In kindergarten, the Cross Number Puzzle format serves as one way to organize sorting and let children capture some "data" from their sorting.
- In first grade, it becomes a kind of "spreadsheet."
- In second and third grades, it structures the development of the addition and subtraction algorithms.
- This PowerPoint does not include the role that the Cross Number Puzzle plays in the development of the multiplication and division algorithms (see Multiplication PowerPoint for that), but does show how the way that Think Math! teaches the logic of addition and subtraction prepares students for high school algebra.

- A second presentation was prepared as an aid in presenting the Cross Number Puzzle format to teachers who are new to Think Math!.