Math lesson plan · 7th grade (Year 8 in England) · 45 minutes
Decrease an amount by a percentage
Decimals and percentages
CCSS 7.RP.A.3England: KS3 NumberEngland: GCSE Foundation Ratio
Objective and success criteria
Students will: Decrease an amount by a percentage.
- 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 of an amount
Leads to: Find the percentage change; Sale prices and discounts; Use decimal multipliers for percentage change
Materials: Place value chart with tenths and hundredths, Hundred squares, Number lines, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Percentage of an amount). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- What is 40% of 30? → 12Prompt: Find 10% (or 1%) first, then build up.
- Find 15% of 380. → 57Prompt: 10% of 380 is 38. What are 5% and 1%?
- There are 440 runners at an event. 30% of them arrive by bike. How many arrive by bike? → 132Prompt: Find 30% of 440.
Hook · 5 min
- Show two prices or race times with decimals and ask which is bigger, then why.
- Share the objective: Decrease an amount by a percentage. 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: Decrease 400 by 50%.
- Step 1: 50% × 400 = 200
- Step 2: 400 − 200 = 200
- Answer: 200
- 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.
- Decrease 640 by 50%. → 320Prompt: Find 50% of 640.
- A household used 750 kWh of electricity last year. This year it cut its use by 6%. How many kWh did it use this year? → 705Prompt: After a 6% decrease, 94% is left.
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.
- A household used 1950 kWh of electricity last year. This year it cut its use by 18%. How many kWh did it use this year? → 1599Prompt: After a 18% decrease, 82% is left.
- Sofia says that to decrease 220 by 20% you multiply by 0.2. Find the correct result of decreasing 220 by 20%. → 176Prompt: Multiplying by 0.2 finds the 20% you take away, not what is left.
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 of an amount.
- 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
- Move on to: Find the percentage change; Sale prices and discounts; Use decimal multipliers for percentage change.
- 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-7.
Free lesson plan from eurekami.com/lesson-plan-builder