Show model answer and explanation
15
23−8.
Class 9 · English Medium · Pearson Edexcel · Mathematics
Data, probability and written reasoning
Use cumulative counts and conditional chance with a clear reference group.
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
Cumulative frequency counts observations up to a threshold. It does not give the number in one interval until neighbouring cumulative counts are subtracted. Conditional probability restricts attention to a specified subgroup.
Worked example
If cumulative counts up to 10 and 20 are 7 and 19, then12 observations lie in (10,20]. If4 of 10 club members cycle, the probability for a randomly chosen member of that club is 4/10.
- 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
1/2
6 of the12 girls cycle.
Show model answer and explanation
3/10
6 of all20 pupils.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
One selects only girls; the other selects from the entire class.
Name both reference groups.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
Individual values within each interval are not shown; midpoint calculations estimate them.
Explain the information loss.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Create a two-way table and write two probabilities with different conditioning groups.
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.