Lesson objective: Add and subtract to solve problems with grams and kilograms using the number line to show the problem solving strategy.

This lesson helps to build procedural skills with whole number addition and subtraction using multiple strategies. A number line is used here because it supports understanding the story of the problem and the meaning of the problem question. The number line also supports reasoning with number relationships and number properties as the problems are solved. This work develops students' understanding that a number line can show how addition and subtraction can be used to solve problems with grams and kilograms.

Students engage in Mathematical Practice 1 (Make sense of problems and persevere in solving them)** **as they use a number line to understand the problem and the meaning of the question. Students use the number line to show their methods of adding and subtracting problems with mass. Students engage in Mathematical Practice 4 (model with mathematics) as they write a number equation to represent their solution process.

**Key vocabulary:**

- grams
- kilograms
- number equation

**Special materials needed:**

- base ten blocks
- number line from 0 to 1,000 for demonstration
- pan balance with 1, 10, 100, and 1,000 gram weights