Math lesson plan · 7th grade (Year 8 in England) · 45 minutes
Add and subtract negative decimals
Number sense
CCSS 7.NS.A.1.DEngland: KS3 Number
Objective and success criteria
Students will: Add and subtract negative decimals.
- 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: Subtract integers by adding the opposite; Add and subtract decimals
Leads to: Multi-step problems with positive and negative numbers
Materials: Place value chart, Base-ten blocks or a number line, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Subtract integers by adding the opposite; Add and subtract decimals). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- 24 − (−3) = ? → 27Prompt: Subtracting a negative is the same as adding a positive.
- 70.4 + 87.17 = ? → 157.57Prompt: Line up the decimal points.
- −22 − 20 = ? → -42Prompt: Rewrite as −22 + (−20).
Hook · 5 min
- Show a number in the news or a price tag and ask what each digit is worth.
- Share the objective: Add and subtract negative decimals. 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: −4.5 + (−5.9) = ?
- Step 1: −4.5 + (−5.9) = −10.4
- Answer: -10.4
- 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.
- −8.7 + (−3.9) = ? → -12.6Prompt: Use the same sign rules as for integers.
- −1.02 − (−1.9) = ? → 0.88Prompt: Change subtraction to adding the opposite.
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.
- 6.6 + (−6.3) = ? → 0.3Prompt: Use the same sign rules as for integers.
- At 6 pm in Calgary it was −0.8 °C. By midnight the temperature had dropped 6.9 °C. What was the temperature at midnight, in °C? → -7.7Prompt: A drop means subtract.
Watch out for
- Reading 1,045 as one thousand four hundred five: point to each place and say its value.
- Thinking a longer number is always bigger, even with decimals (0.45 vs 0.5).
Support and stretch
Support
- Review first: Subtract integers by adding the opposite.
- Use concrete materials: place value chart.
- 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: Multi-step problems with positive and negative numbers.
- 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