NEB Class 12 • Mathematics • Probability • Practice Set

Conditional Probability & Combinatorial Probability Practice Set: NEB 12 Maths

Master Conditional Probability and Combinatorial Probability through clear concepts, representations, a reliable answer method and exam-focused practice.

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Concepts · Worked reasoning · NEB practice

Quick answer: Conditional probability updates a sample space after information is known. Combinatorial probability counts favorable and total outcomes carefully, while Bayes-style reasoning reverses conditions using base rates.

Worked practice

Build the result from meaning, not memory

Conditional probability updates a sample space after information is known. Combinatorial probability counts favorable and total outcomes carefully, while Bayes-style reasoning reverses conditions using base rates.

Worked example

From a deck, given that a card is a face card, P(king|face)=4/12=1/3.

The governing relationship is P(A|B)=P(A∩B)/P(B); P(A∩B)=P(A|B)P(B); independence means P(A|B)=P(A). Check the convention, geometry or boundary condition before calculation.

Independent practice ladder

  1. Define the key physical quantities and give their SI units.
  2. Draw and label the relevant wave, ray, mode or energy diagram.
  3. Recalculate the worked example after changing one input by a factor of two.
  4. Explain the result without equations.
  5. Create a Nepal-relevant situation such as a classroom speaker, musical pipe, optical slit or thermal machine.
  6. Compare two cases and predict the larger output before calculating.
  7. Find and repair one deliberately wrong sign, node or unit.
  8. Write a three-mark answer and a five-mark answer.

Answer protocol: diagram → known data → principle → symbolic equation → SI substitution → result → physical check. Confusing P(A|B) with P(B|A), cancelling without conditioning the sample space, assuming independence, or counting ordered outcomes as unordered.

NEB answer method

Model → evidence → equation → check

First identify the system and what the question asks. Label the diagram, apparatus or reaction with SI quantities, then state the principle before selecting an equation. Solve symbolically where possible and check units, limiting cases and chemical or physical meaning.

StageQuestionEvidence
ModelWhat is idealised?Assumption stated
RepresentationWhich diagram fits?Labels or balanced equation
CalculationWhich relation follows?Symbols then SI values
EvaluationDoes it make sense?Unit, sign and trend check

Make the idea concrete in Nepal

Connect the model to a school laboratory, household technology, health, environment, energy or local material. The example should clarify the science rather than merely mention a place. Compare a prediction with an observation and record uncertainty.

Review the NEB Class 12 Mathematics revision roadmap and the complete Mathematics guide. For online or physical tuition, call 9846662070.

Questions students ask about Conditional Probability and Combinatorial Probability

What is the central idea of Conditional Probability and Combinatorial Probability?

Conditional probability updates a sample space after information is known. Combinatorial probability counts favorable and total outcomes carefully, while Bayes-style reasoning reverses conditions using base rates.

Which equation should I remember?

P(A|B)=P(A∩B)/P(B); P(A∩B)=P(A|B)P(B); independence means P(A|B)=P(A).

How should I begin a numerical?

Draw the situation, list known quantities in SI units, choose the governing relation symbolically, substitute once and finish with a unit and reasonableness check.

What is a common exam mistake?

Confusing P(A|B) with P(B|A), cancelling without conditioning the sample space, assuming independence, or counting ordered outcomes as unordered.

How can I practise this topic?

Alternate one concept explanation, one diagram and two numericals. Revisit errors after a day instead of only rereading the solution.

Where can I get tuition support?

For online or physical KTM Tuition classes, call 9846662070. After Grade 12, the MKS Education panel below gives preparation and pre-counselling contacts.

Frequently asked questions

References and next steps

Scope checked against CDC Nepal; concept support from an institutional reference and OpenStax Science. Continue with the Conditional Probability and Combinatorial Probability cluster.

NEB +2 tuition support

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