Equations as balanced scales
KS3 · 35 minutes · Solve a two-step linear equation and check by substitution.
Answer by: Type. You can change method or take a break at any time.
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Our learning goal
Solve a two-step linear equation and check by substitution.
Your turn: Choose one thing you would like to understand by the end.
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My lesson notes & project
Full teaching script
- Today: Equations as balanced scales. Our goal: Solve a two-step linear equation and check by substitution.
- Take one idea at a time. Pause after each sentence; ask for repetition whenever you need it.
- An equation says that two expressions have the same value. In 3x + 5 = 20, x is an unknown number. Subtract five from both sides to keep the equality: 3x = 15. Divide both sides by three: x = 5. Check in the original equation: 3 × 5 + 5 = 20. The check matters because a neat-looking method can still contain a mistake. For 4x − 7 = 9, add seven to both sides to get 4x = 16, then divide by four to get x = 4. We reverse the addition or subtraction first, then the multiplication. Do not subtract five from only one side; that changes the balance. Writing each step on a new line makes reasoning easier to check.
- Together: choose one example from the explanation and show how it works. What do you notice?
- Your turn: Model 3x + 5 = 20. Solve 2x + 3 = 11 together. Independently solve 5x + 2 = 27, 4x − 7 = 9 and 6x + 1 = 19. Substitute each answer.
- Reflect: what made sense, and what would you like explained differently?
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