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.
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