Lesson objective: Solve problems using a number line to show addition and subtraction methods for solving one step liquid volume problems.
This lesson provides an opportunity for students to apply their knowledge and understanding of adding and subtracting milliliters to a reallife situation. Students are asked to show their method for solving liquid volume problems on the number line.
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 involving addition within 1,000 is provided in the Additional Materials section of the lesson.
Key Concept students will use:

representations and drawings to solve onestep situational problems involving addition and subtraction of liquid volumes.
Skills students will use:
 a number line to solve many types of addition and subtraction problems (Grade 2, Unit3, Unit 8)
 compose or decompose tens or hundreds when adding or subracting threedigit numbers (Grade 2, Unit 11)
 place value understanding to add and subtract using a variety of strategies (Grade 3, Unit 3).
Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them) as they use the number line and pictures to show their methods for adding and subtracting to solve liquid volume problems. Students engage in Mathematical Practice 4 (Model with mathematics) as they write number equations to explain their methods for solving the problem.
Key vocabulary:
 liters
 liquid volume
 milliliters
 number line
Special materials needed:
 base ten blocks units, rods, flats, blocks
 number line for demonstrating placement of numbers between 100's