Show model answer and explanation
400
500/1.25.
Class 10 · English Medium · Cambridge · Mathematics
Number, fractions, decimals and percentages
Reverse a percentage change and interpret rounding intervals.
About this lesson and its coverage
Original Kidemy Class 10 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
To undo a percentage increase, divide by its scale factor rather than subtracting the same percentage. A rounded measurement represents an interval of possible values under a stated rounding convention.
Worked example
After20% increase a price is 360: original360/1.2=300. A length rounded to nearest cm as12 has interval11.5≤L<12.5 cm under the usual half-up boundary convention.
- 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.
Show model answer and explanation
90
72/0.8.
Show model answer and explanation
7.5
The boundary is half a unit below.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
The reduction uses360 as its base and gives 288; undoing the rise requires division by 1.2.
Explain both bases.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
4.55≤m<4.65 kg under the stated convention.
Use half the rounding step and appropriate endpoints.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Solve a reverse-change problem and explain the precision of the supplied data.
Review with a guardian or teacher
- Use the stated evidence or givens.
- Show reasoning rather than only a result.
- Review and explain one correction.
Keep your work on paper or in a local file. This page does not upload it or automatically grade the project.
Teacher-led lessons, schedules and prices for this outline are upcoming. You can use any starter practice above now without booking.
Your next step
Solo practice works without an account. Sign in to save a practice record to your learner profile.
Keep practising
Exact lesson links and related activities are labelled separately. Return-to-course links retain your selected learning path.