Which One Doesn’t Belong? Addition Tables

Look at this set of four pictures. Decide which one doesn’t belong with the other three. Use math words to describe your thinking. There are many ways to think about each one!

4 addition tables with 11 rows and 11 columns. A. A diagonal line of shaded numbers from 0 to 20. B. 2 diagonal lines of shaded numbers from 1 to 19. C. A diagonal line with all the 10's shaded. D. Shaded numbers 11 to 20 on the bottom row and 11 to 20 in the last column.


Find reasons why each of the pictures might not belong with the other three.


Explain your thinking to someone else. Do they have different reasons why one doesn't belong?