medium difficulty5 min

Chance and Likelihood

Chance and likelihood describe how possible an event is, using words such as certain, impossible, likely, unlikely, and equally likely.

In one line: Unlikely is not impossible; it only means less chance.

Practice This Concept

Understand it

Before writing probability as a number, students should judge the situation sensibly.
If an event must happen, it is certain.
If it cannot happen, it is impossible.
If it has a better chance than another event, it is more likely.

Example

Getting a number less than 7 on a normal die is certain, while getting 8 on the same die is impossible.

Formula and rule

Use language first: impossible means no chance, certain means must happen, likely means better chance, and unlikely means smaller chance.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

For a bag with 8 red balls and 2 blue balls, picking a red ball is more likely than picking a blue ball because red balls are more in number.

Method you can reuse

Identify the event, check whether it can happen, compare favourable cases with other cases, and then choose the correct likelihood word.

Visual tip

A simple chance line from impossible to certain can help compare events in order.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

On a normal die, is getting an even number impossible, unlikely, likely, or certain?

Think first, then show answer

Getting an even number on a normal die is likely but not certain, because 2, 4, and 6 are possible outcomes out of six total outcomes.

Common wrong answer

Calling blue impossible in a bag with 8 red and 2 blue balls.

Why it loses marks: Blue balls are present, though fewer.

Don't mix this up

Students often call an event impossible just because it is unlikely. Unlikely means it can still happen, but with a small chance.

Exam tip

Read the condition carefully and decide whether the event can happen, must happen, or may happen before assigning a probability idea.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions may ask students to classify everyday events as certain, impossible, likely, or unlikely, with a short reason.

1
Enough for 1 mark
Chance and likelihood describe how possible an event is, using words such as certain, impossible, likely, unlikely, and equally likely.
2
Add for 2 marks
Example: Getting a number less than 7 on a normal die is certain, while getting 8 on the same die is impossible.
3
Add for 3 marks
If an event must happen, it is certain.

MCQ Quiz

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