In this lesson, students continue exploring patterns among familiar facts on the addition chart. They examine patterns in expressions where the totals are the same. For example, given the sequence 5 + 5, 4 + 6, 3 + 7, 2 + 8, and 9 + 1, which forms a "staircase" on the addition chart, they notice that the total is 10 each time. Moreover, there are other staircases on the addition chart containing expressions that share the same total.