Lesson objective: Solve problems using the number line to show addition and subtraction strategies.
This lesson provides an opportunity for students to apply their knowledge and understanding of addition and subtraction to a reallife situation. Students are asked to show on the number line a correct strategy for solving the problem.
Note that in the number selection in this lesson asks students to add and subtract beyond 1000, exceeding the gradelevel expectations for Grade 3. An alternate task with addends within 1,000 is included in the Additional Materials.
Key Concept students will use:

representations and drawings to solve onestep situational problems involving addition and subtraction of mass.
Skills students will use:
 place value understanding to add and subtract using a variety of strategies (Grade 3, Unit 3)
 a number line to solve many types of addition and subtraction problems (Grade 2, Unit 2)
 representations of a threedigit number as hundreds, tens, and ones, from left to right. (Grade 2, Unit 6)
Students engage in Mathematical Practice 1 (make sense of problems and persevere in solving them) as they use the number line to understand the problem and the meaning of the question. Students engage in Mathematical Practice 4 (model with mathematics) as they write number equations to describe how they used the number line.
Key vocabulary:
 grams
 kitchen gram scale
 number line
 pan balance
Special materials needed:
 kitchen gram scale
 number line for demonstration (0 to 2,000)
 pan balance scale and gram weights