Math lesson plan · 9th grade (Year 10 in England) · 45 minutes
Ratio problems with algebra
Ratio and proportion
CCSS HSA.CED.A.1England: GCSE Higher Ratio
Objective and success criteria
Students will: Ratio problems with algebra.
- 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: Share in a given ratio; Two-step equations
Leads to: the next skill in this area.
Materials: Bar models, Double number lines, Ratio tables, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Share in a given ratio; Two-step equations). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Tariq and Amara share $49 in the ratio 4:3. How much does Amara get? (Type the number only.) → 21Prompt: How many parts are there altogether?
- The ratio of adults to children at a show is 4:5. There are 10 more children than adults. How many people are there in total? → 90Prompt: The difference in parts is 1.
- Sofia and Chloe share $30 in the ratio 2:3. How much does Sofia get? (Type the number only.) → 12Prompt: How many parts are there altogether?
Hook · 5 min
- Share a recipe for 4 people and ask how much is needed for 6.
- Share the objective: Ratio problems with algebra. 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: The ratio x : y is 3 : 4, and y is 2 more than x. Find x.
- Step 1: 4x = 3(x + 2)
- Step 2: 4x = 3x + 6
- Step 3: x = 6
- Step 4: x = 6
- Answer: x = 6
- 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.
- The ratio x : y is 4 : 9, and y is 45 more than x. Find x. → x = 36Prompt: Write y as x + 45. Then x/(x + 45) = 4/9.
- (x + 2) : (3x + 1) = 2 : 5. Find x. → x = 8Prompt: Write the ratios as fractions and cross-multiply.
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.
- The ratio x : y is 3 : 7, and y is 20 more than x. Find x. → x = 15Prompt: Write y as x + 20. Then x/(x + 20) = 3/7.
- (x + 7) : (2x + 17) = 3 : 7. Find x. → x = 2Prompt: Write the ratios as fractions and cross-multiply.
Watch out for
- Adding the same amount to both parts instead of multiplying.
- Mixing up part-to-part and part-to-whole ratios.
Support and stretch
Support
- Review first: Share in a given ratio.
- Use concrete materials: bar models.
- 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