Lesson objective: Solve a complex problem using efficient strategy choices for addition and subtraction.

This lesson provides an opportunity for students to apply their knowledge and understanding of addition, subtraction, and estimation to a real-life situation. Students are asked to create a cargo load for their shuttle to Mars for three astronauts. The criteria include a minimum and maximum weight load and some items that must be included in the cargo. The rest of the load is made up with choices that students can make.

Key Concept students will use:

- The standard algorithms for addition and subtraction are efficient ways to add and subtract that use place value concepts.

Skills students will use:

- add and subtract using the standard algorithms (Grade 4, Unit 4)
- add and subtract using mental math and number decomposition (Grade 4, Unit 4)
- estimate using rounding (Grade 4, Unit 4)

Students engage in Mathematical Practice #1, make sense of problems and persevere in solving them as they analyze the task and make choices about the best way to arrive at the solution. Students should carefully examine the criteria for the problem and make strategic decisions in order to reach a solution with the expected weight range. Students engage in Mathematical Practice #2, reason abstractly and quantitatively as they make choices about strategies for solving various addition and subtraction problems based on the numbers within the problem. Students should examine the numbers and operations within a problem and determine if the standard algorithm is the most efficient strategy to use or if another strategy (mental math) would be more efficient.

**Key vocabulary: **

- decompose
- essential
- justify
- optional
- standard algorithm
- strategy