NCERT Solutions for Class 9th Maths Chapter 7 The Mathematics of Maybe: Introduction to Probability
Updated on 2026-09-08
About this chapter
Probability measures how likely an event is , on a scale from 0 to 1. For an event E, 0 ≤ P(E) ≤ 1. P(E) = 0 means impossible, P(E) = 1 means certain, P(E) = 1/2 means an even chance. Nothing outside [0, 1] is a probability. A random experiment is one you can repeat, whose full list of possible results you know in advance, but whose result on any single trial you cannot know. The complete list of possible results is the sample space S ; each item in it is an outcome ; the number of items is the sample size n(S) . An event is any subset of S — one outcome, several outcomes, or none. Experimental probability = (number of times the event occurred) ÷ (total number of trials). It is a relative frequency — it describes the data you have, so different sets of trials give different values. Theoret
- What is Probability?
- What is Randomness?
- The Probability Scale
- Analysing Statistical Data Using Probability
- Measuring Probability Objectively
- Sample Space
- Elements of Probability: Sample Spaces and Events
- Tree diagrams
- Chapter 7 review (questions marked * are the harder set)
Exercises
- In-text Questions — What is Probability? Page 155
- Think and Reflect — What is Randomness? Page 156
- In-text Questions — What is Randomness? Page 157
- Think and Reflect — What is Randomness? Page 157
- Exercise Set 7.1 — The Probability Scale Page 159
- Think and Reflect — Analysing Statistical Data Using Probability Page 163
- Exercise Set 7.2 — Measuring Probability Objectively Page 165–166
- Think and Reflect — Sample Space Page 167
- Exercise Set 7.3 — Elements of Probability: Sample Spaces and Events Page 167–168
- Think and Reflect — Tree diagrams Page 169
- Exercise Set 7.4 — Tree diagrams Page 169
- Chapter 7 review (questions marked * are the harder set) — End-of-Chapter Exercises Page 169–173