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5.Probability Basics
Class 11 • Mathematics • NCERT
Probability Basics
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This lesson introduces the basic idea of probability as prescribed by NCERT Class 11. Students learn how to calculate probability using the classical approach and understand key concepts like favourable outcomes and certainty.
Lesson Objectives
- Understand the meaning of probability.
- Learn the classical definition of probability.
- Calculate probability of simple events.
- Interpret probability values correctly.
1. What Is Probability?
Probability is a measure of how likely an event is to occur.
Probability helps us make predictions about uncertain situations.
2. Classical Definition of Probability
If an experiment has a finite number of equally likely outcomes, then:
P(E) = (Number of favourable outcomes) / (Total number of outcomes)
3. Favourable and Total Outcomes
Favourable outcomes are outcomes that satisfy the given event.
Example: Rolling a die
Event: Getting an even number
Favourable outcomes = {2,4,6}
Event: Getting an even number
Favourable outcomes = {2,4,6}
4. Probability Scale
The value of probability always lies between 0 and 1.
0 ≤ P(E) ≤ 1
• P(E) = 0 → Impossible event
• P(E) = 1 → Sure event
5. Simple NCERT Examples
• Probability of getting head in a coin toss = 1/2
• Probability of getting a 7 on a die = 0
Practice Questions (NCERT)
- Define probability.
- Write the classical definition of probability.
- What are favourable outcomes?
- What is the probability of a sure event?
- What is the probability of an impossible event?
- Find the probability of getting a tail when a coin is tossed.
- Find the probability of getting an odd number on a die.
- Can probability be negative?
- Can probability be greater than 1?
- Is this topic part of NCERT Class 11 syllabus?
✅ Show Answer Key
- Measure of likelihood of an event
- Favourable outcomes / Total outcomes
- Outcomes satisfying the event
- 1
- 0
- 1/2
- 3/6 = 1/2
- No
- No
- Yes
© Aviate Learning – Probability (NCERT Class 11)