Show model answer and explanation
0.3
0.18/0.6.
Class 12 · English Medium · Cambridge · Mathematics
Data, probability and written reasoning
Use conditional probabilities and transform a random variable’s mean and spread.
About this lesson and its coverage
Original Kidemy Class 12 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
Conditional probability changes the reference event: P(A|B)=P(A∩B)/P(B) when P(B)>0. If Y=aX+b, its mean becomes aE(X)+b and variance a²Var(X). Variance measures squared spread; adding a constant shifts location without changing spread.
Worked example
If E(X)=4 and Var(X)=9, then Y=2X+1 has mean9 and variance36. This describes a model’s average and squared variability, not an individual outcome.
- 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
13
3×5−2.
Show model answer and explanation
36
3²×4.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
The mean also rises by 7, so each deviation from the mean stays the same.
Explain deviation, not only quote a rule.
Write in your own words. A guardian or teacher should review this response.
Show model answer and explanation
There is no positive-probability reference group B to divide by.
State the denominator condition.
Progress and browser storage
Notebook challenge, sources and further study
Apply the idea
Create a two-way probability table and explain two conditional results.
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.