Illustrative Mathematics Unit 6.6, Lesson 3: Staying in Balance

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Illustrative Math
Grade 6

Lesson 3: Staying in Balance

Let’s use balanced hangers to help us solve equations.

Illustrative Math Unit 6.6, Lesson 3 (printable worksheets)

Lesson 3 Summary

A hanger stays balanced when the weights on both sides are equal. We can change the weights and the hanger will stay balanced as long as both sides are changed in the same way. For example, adding 2 pounds to each side of a balanced hanger will keep it balanced. Removing half of the weight from each side will also keep it balanced.
An equation can be compared to a balanced hanger. We can change the equation, but for a true equation to remain true, the same thing must be done to both sides of the equal sign. If we add or subtract the same number on each side, or multiply or divide each side by the same number, the new equation will still be true.
This way of thinking can help us find solutions to equations. Instead of checking different values, we can think about subtracting the same amount from each side or dividing each side by the same number.
The following diagram shows how to write equations that could represent the weights on a balanced hanger.

Lesson 3.1 Hanging Around

1. For diagram A, find:
   a. One thing that must be true
   b. One thing that could be true or false
   c. One thing that cannot possibly be true
   
2. For diagram B, find:
   a. One thing that must be true
   b. One thing that could be true or false
   c. One thing that cannot possibly be true
   

• See Video for Whole Lesson

Scroll down the page for the solutions to the “Are you ready for more?” section.

Lesson 3.2 Match Equations and Hangers

1. Match each hanger to an equation. Complete the equation by writing x, y, z, or w in the empty box.
2. Find a solution to each equation. Use the hangers to explain what each solution means.

Lesson 3.3 Connecting Diagrams to Equations and Solutions

Here are some balanced hangers. Each piece is labeled with its weight.
For each diagram:

1. Write an equation.
   
2. Explain how to reason with the diagram to find the weight of a piece with a letter.
   
3. Explain how to reason with the equation to find the weight of a piece with a letter.

Are you ready for more?

When you have the time, visit the site https://solveme.edc.org/Mobiles.html to solve some trickier puzzles that use hanger diagrams like the ones in this lesson. You can even build new ones. (If you want to do this during class, check with your teacher first!)

Lesson 3 Practice Problems

1. Select all the true equations.
   A. x + x + x = 1 + 1 + 1 + 1 + 1 + 1
   B. x · x · x = 6
   C. 3x = 6
   D. x + 3 = 6
   E. x · x · x = 1 · 1 · 1 · 1 · 1 · 1
   
2. Write an equation to represent each hanger.
   
3. a. Write an equation to represent the hanger.
   b. Explain how to reason with the hanger to find the value of x.
   c. Explain how to reason with the equation to find the value of x.
   
4. Andre says that x is 7 because he can move the two 1s with the x to the other side.
   
5. Match each equation to one of the diagrams.
   
6. The area of a rectangle is 14 square units. It has side lengths a and b. Given the following values for a, find b.
   a = 2 1/3
   a = 4 1/5
   a = 7/6
   
7. Lin needs to save up $20 for a new game. How much money does she have if she has saved the following percentages of her goal? Explain your reasoning.
   a. 25%
   b. 75%
   c. 125%

The Open Up Resources math curriculum is free to download from the Open Up Resources website and is also available from Illustrative Mathematics.

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