Math lesson plan · 9th grade (Year 10 in England) · 45 minutes
Error intervals and bounds
Number sense
CCSS HSN.Q.A.3England: GCSE Foundation NumberEngland: GCSE Higher Number
Objective and success criteria
Students will: Error intervals and bounds.
- 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: Round decimals
Leads to: the next skill in this area.
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 (Round decimals). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Round 68.468 to 2 decimal places. → 68.47Prompt: Find the digit in the place you are rounding to.
- Leo's lunch costs $2.92. Round the cost to the nearest whole dollar. (Type the number only.) → 3Prompt: Look at the digit after the decimal point.
- Round 44.729 to the nearest whole number. → 45Prompt: Find the digit in the place you are rounding to.
Hook · 5 min
- Show a number in the news or a price tag and ask what each digit is worth.
- Share the objective: Error intervals and bounds. 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: A measurement is 13.4 kg, correct to 1 decimal place. What is the upper bound?
- Step 1: 13.4 + 0.05 = 13.45
- Answer: 13.45
- 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.
- A measurement is 35 cm, correct to the nearest whole number. What is the lower bound? → 34.5Prompt: Rounding to 1 means the true value is within half of 1 either side.
- A rectangle measures 14 cm by 7 cm, each to the nearest cm. What is the upper bound of its area, in cm²? → 108.75Prompt: Find the upper bound of each length first.
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 rectangle measures 20 cm by 7 cm, each to the nearest cm. What is the upper bound of its area, in cm²? → 153.75Prompt: Find the upper bound of each length first.
- A measurement is 7.8 cm, correct to 1 decimal place. What is the lower bound? → 7.75Prompt: Rounding to 0.1 means the true value is within half of 0.1 either side.
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: Round decimals.
- 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
- 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