TIP: Use white to remove color from individual squares. Swipe across horizontally or vertically to color an entire row or column. Select a number from the top and left rows to see the sum (dark gray). Select the + sign to see all the doubles sums.
Interactive Addition Chart - Learning Connections
Mental Math - visualize addition patterns
Common Core Connections - Grades K to 2
Add and subtract with 20.
Commutative property of addition.
Look for and make use of structure.