Math lesson plan · 9th grade (Year 10 in England) · 45 minutes
Solve multi-step inequalities, including reversing the sign
Algebra
CCSS HSA.REI.B.3England: GCSE Foundation AlgebraEngland: GCSE Higher Algebra
Objective and success criteria
Students will: Solve multi-step inequalities, including reversing the sign.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Solve linear inequalities
Leads to: Find the error in a worked inequality; Solve double inequalities like a < bx + c < d; Solve 'or' compound inequalities
Materials: Balance scales or a balance drawing, Algebra tiles, Function machine cards, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Solve linear inequalities). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Solve: 5x + 9 < 44 (x < 35 / x > 7 / x < 7 / x < 8) → x < 7Prompt: Solve it like an equation, keeping the inequality sign.
- Solve: −6x − 7 ≤ −25 (x ≤ −3 / x ≤ 3 / x ≥ −3 / x ≥ 3) → x ≥ 3Prompt: Isolate the x term first.
- What is the smallest whole number x that satisfies 6x + 8 ≥ 17? → 2Prompt: Solve the inequality first.
Hook · 5 min
- Show a "think of a number" puzzle and ask the class to work out the starting number.
- Share the objective: Solve multi-step inequalities, including reversing the sign. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Solve: x + 8 ≥ 15
- Step 1: x ≥ 7
- Step 2: x ≥ 7
- Answer: x ≥ 7
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Solve: −6x + 9 < 45 (x > −5 / x > 6 / x > −6 / x < −6) → x > −6Prompt: Solve it like an equation, step by step.
- Solve: −(x + 1) < −5x − 21 (x < 5 / x > −5 / x < −3 / x < −5) → x < −5Prompt: Expand the bracket, then collect x terms on one side.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- What is the greatest integer that satisfies −x − 2 > 2? → -5Prompt: Solve the inequality first.
- Solve: -5(x + 5) ≥ 2x − 53 (x ≤ −4 / x ≤ 6 / x ≥ 4 / x ≤ 4) → x ≤ 4Prompt: Expand the bracket, then collect x terms on one side.
Watch out for
- Doing an operation to one side of an equation but not the other.
- Reading 3x as 3 + x, or thinking x always stands for one particular number.
Support and stretch
Support
- Review first: Solve linear inequalities.
- Use concrete materials: balance scales or a balance drawing.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Move on to: Find the error in a worked inequality; Solve double inequalities like a < bx + c < d; Solve 'or' compound inequalities.
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-9.
Free lesson plan from eurekami.com/lesson-plan-builder