Grades: K‒4

Students add two-digit and three-digit numbers on an open number line (a number line that only displays the location of 0). They devise different strategies for decomposing and composing the addends to make it easier to find their sum. These strategies include using landmark numbers, jumping by multiples of ten, and splitting addends into smaller “friendlier” numbers.

OBJECTIVES

- Students will use an open number line model to add two- and three-digit numbers.
- Students will see the relationship between the pictorial representation of addition and its symbolic form.
- Students will develop strategies for adding numbers by decomposing and composing them in ways that make them easier to add. These strategies should be applicable across multiple models and problem types, and should include using landmark numbers, jumping by multiples of ten, and splitting addends into smaller “friendlier” numbers.

COMMON CORE CONNECTIONS

Mathematical Practices

(1) Make sense of problems and persevere in solving them; (2) Reason abstractly and quantitatively; (3) Construct viable arguments and critique the reasoning of others; (4) Model with mathematics; (5) Use appropriate tools strategically; (7) Look for and make use of structure.

Content Standards

1.NBT5,6; 2.OA2; 2.NBT5, 6, 7, 8, 9; 3.NBT2

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