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2
72/36.
O Level · English Medium · Cambridge · Mathematics
Ratio, proportion and algebra
Model variation and manipulate algebraic expressions safely.
About this lesson and its coverage
Original Kidemy O Level progression. This level has its own text, examples and questions. Curriculum versions share the progression; complete board-specific coverage still needs specification matching and additional material.
Learn the idea
Distinguish a formula from a numerical equation. Factor before cancellation and retain excluded values. A variation model’s constant is tied to the chosen units; changing units can change its numerical value.
Worked example
For y=kx² and pair(3,45), k=5. For (2x²−8)/(x−2), simplification gives 2x+4 with x≠2.
- Identify the quantities and restrictions.
- Show a method with units or symbols.
- Check and explain the result.
Your written practice
Show your working on paper. Check your answer, then choose Next.
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6
x=30/5.
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x²+8x
4x²+8x−3x².
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x+5 for x≠5.
Factor and preserve the domain.
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Show model answer and explanation
Different units change the numerical comparison;2m:50 cm becomes200:50=4:1.
Use a concrete unit conversion.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Solve an algebraic model and explain every restriction and unit choice.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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