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5
50=25×2.
Class 9 · English Medium · Cambridge · Mathematics
Number, fractions, decimals and percentages
Simplify surds and calculate compound changes with exact intermediate values.
About this lesson and its coverage
Original Kidemy Class 9 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
A surd keeps a root exact. Factor out square factors before combining like surds. Compound percentage changes multiply scale factors; early rounding can introduce avoidable errors.
Worked example
√72=6√2. A 500 amount growing4% twice is 500×1.04²=540.8.
- Identify the quantities and restrictions.
- Show a method with units or symbols.
- Check and explain the result.
Your written practice
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1210
1000×1.1².
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3
The square reverses the positive square root.
Write in your own words. A guardian or teacher should review this response.
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3√2+2√2=5√2.
Show the square factors.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
It avoids accumulating rounding error before the final result.
Distinguish exact working from justified final precision.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Compare an exact calculation and a rounded intermediate calculation, explaining any difference.
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- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
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