Math lesson plan · 8th grade (Year 9 in England) · 30 minutes
Reverse percentages
Decimals and percentages
CCSS 7.RP.A.3England: GCSE Foundation RatioEngland: GCSE Higher Ratio
Objective and success criteria
Students will: Reverse percentages.
- 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: Percentage increase and decrease
Leads to: the next skill in this area.
Materials: Place value chart with tenths and hundredths, Hundred squares, Number lines, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 4 min
- Quick retrieval from earlier learning (Percentage increase and decrease). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- A bike costs $180. In a sale it is 50% off. What is the sale price? (Type the number only.) → 90Prompt: Find 50% of 180 first.
- Increase 940 by 15%. → 1081Prompt: Find 15% of 940 and add it on.
- A value changes from 220 to 110. What is the percentage decrease? → 50Prompt: Find the change first.
Hook · 3 min
- Show two prices or race times with decimals and ask which is bigger, then why.
- Share the objective: Reverse percentages. Read the success criteria together.
I do: model it · 7 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: After a 20% discount, a jacket costs $432. What was the original price? (Type the number only.)
- Step 1: 80% → 432
- Step 2: 1% → 5.4
- Step 3: 100% → 540
- Answer: 540
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 6 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- After a 10% discount, a jacket costs $360. What was the original price? (Type the number only.) → 400Prompt: The sale price is 90% of the original.
- A price includes 5% tax and is $546. What was the price before tax? (Type the number only.) → 520Prompt: The new price is 105% of the original.
You do: independent practice · 7 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 6 questions are on the student sheet below, with answers in the key.
Exit ticket · 3 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- A price includes 5% tax and is $252. What was the price before tax? (Type the number only.) → 240Prompt: The new price is 105% of the original.
- After a 10% discount, a jacket costs $162. What was the original price? (Type the number only.) → 180Prompt: The sale price is 90% of the original.
Watch out for
- Thinking 0.45 is bigger than 0.5 because 45 is bigger than 5.
- Moving the digits the wrong way when multiplying or dividing by 10.
Support and stretch
Support
- Review first: Percentage increase and decrease.
- Use concrete materials: place value chart with tenths and hundredths.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- 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-8.
Free lesson plan from eurekami.com/lesson-plan-builder