## Stability in Numbers

• Lesson
3-5
1

In this lesson, students apply their knowledge of addition equations to create number sentences using an electronic balance tool.

To begin the lesson, ask students what an addition sentence or addition equation looks like. They might respond with, 9 + 7 = 16. Students should notice there are two addends, the addition symbol, the equal symbol, and a sum. Students may share other examples, as necessary.

Introduce the Pan Balance - Numbers Tool to the students.

 Pan Balance - Numbers

Put 4 onto the left pan by typing in the red space above the pan. Ask students, "What happens? Why?"

Now put 9 onto the blue right pan by typing in the space above the pan. Ask students, "What happens? Why?"

Note: These two steps help introduce students to the mechanics of the electronic tool.

Next, pose the following scenario to students:

What number sentences can you create using the number 12?

First reset the balance. Put 12 into the right pan. Now put a sum (two numbers added together) onto the left pan that will balance with 12. Ask students why the pan balanced.

Next, show another sum that balances with 12. Ask students, "How many sums can you find?" Students may indicate the following sums:

0 + 12
1 + 11
2 + 10
3 + 9
4 + 8
5 + 7
6 + 6

This would also be an appropriate time to review the commutative property of addition, namely 3 + 9 has the same sum as 9 + 3.

Next put 3 + 9 on the left pan. Put something onto the right pan that will make it balance. Then find something else that will balance with 3 + 9. Ask students, "Why does this work? How many answers can you find?" Students may indicate the following sums:

7 + 5
6 + 6
and so on...

As necessary, share more examples with the class. When you have finished the whole-class demonstration and exploration, students should work in pairs to use the the Pan Balance - Numbers Tool.

 Pan Balance - Numbers

Distribute the Addition Equations activity sheet to each pair of students.

Students should work together to complete the five activities on the activity sheet.

Assessments

Collect the the Addition Equations activity sheets from each pair of students. Use the responses on the activity sheet to assess student understanding.

Extensions

1. The operations of subtraction and division can be used in the expression balance as well. The shape balance equations can be translated directly into number sentences which emphasize the relationship role of the equals sign.
2. The expression balance can also be used to verify number sentences such as:
3 × (5 - 2) = 15 - 6.

Use * for multiplication, / for division, and - for subtraction on your keypad.

3. Ask students, "What is the largest number of numbers that you can use to balance with 12? What is the smallest number of numbers?"

Questions for Students

Can you add up three numbers to get a sum of 12? Four numbers?

### Learning Objectives

Students will:

• Investigate the equivalence of two numeric expressions
• Create and solve addition equations

### Common Core State Standards – Practice

• CCSS.Math.Practice.MP1
Make sense of problems and persevere in solving them.
• CCSS.Math.Practice.MP4
Model with mathematics.
• CCSS.Math.Practice.MP5
Use appropriate tools strategically.
• CCSS.Math.Practice.MP7
Look for and make use of structure.