Class 11 Maths Chapter 14 Probability – Revision Notes

Probability in Chapter 14 of Class 11 Maths is built on a simple ratio: favourable outcomes divided by the total outcomes in the sample space. This page runs through the terminology, event types, and the addition rule used when combining two events.

Last Updated: September 23, 2026

Key Terms

• Random experiment; Sample space (S); Event = subset of S.

Event Types

• Impossible (∅): P=0. Sure (S): P=1.
• Complement: P(A’)=1−P(A).
• Mutually exclusive: no overlap.

Probability Formula

• P(A) = n(A)/n(S); 0≤P(A)≤1.

Addition Rule

• P(A∪B) = P(A)+P(B)−P(A∩B).
• Mutually exclusive: P(A∪B)=P(A)+P(B).

One-Line Summary

Theoretical probability is calculated as favourable outcomes over total outcomes in the sample space, with the addition rule handling combined events by subtracting any overlap to avoid double-counting.

Quick visual: a worked diagram from the full Solutions page, for reference.

Frequently Asked Questions

What is the difference between mutually exclusive and independent events in probability?
Mutually exclusive events cannot occur at the same time, like getting a 2 and a 5 on a single die roll, while independent events are ones where the occurrence of one does not affect the probability of the other, like flipping a coin twice.

How is the probability of an event calculated using the axiomatic approach introduced in this chapter?
Probability is assigned to each outcome of a sample space as a number between 0 and 1 such that the probabilities of all outcomes sum to 1, and the probability of an event is the sum of probabilities of its favourable outcomes.

Written by Satish

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