Topics
13. Probability
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AustraliaNSW
Stage 3

13.01 Describe likelihood

Lesson
Practice
Lesson

Are you ready?

What words can you think of that describe the the chance of something happening? Can you think of examples of events that fit each word you can think of?

Examples

Example 1

What is the chance my paper plane will fly forever?

A
Impossible
B
In between certain and impossible
C
Certain
Worked Solution
Create a strategy

Think about if a paper plane can fly forever.

Apply the idea

A paper plane must eventually land so it is impossible that it will fly forever. The answer is option A.

Idea summary

These are the 2 terms we have seen to describe chance:

  • Impossible: definitely will NOT happen.

  • Certain: definitely will happen.

Words to describe chance

This video looks at 5 words to describe probability. Impossible, Unlikely, Even chance, Likely and Certain. We order these on a line similar to a number line.

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Examples

Example 2

Which section describes the chance of 'the next person you meet has the same birthday as you'?

This image shows Impossible, Even chance and Certain on a chart. Ask your teacher for more information.
A
A purple square with lines on it.
B
A green square with lines on it.
Worked Solution
Create a strategy

Think about how often you meet someone with the same birthday as you.

Apply the idea

It is unlikely that the next person you meet has the same birthday as you.

An unlikely event will have a chance between impossible and even chance, which is described by the purple section.

The correct option is A.

Idea summary

More terms to describe chance:

  • Unlikely: more likely NOT to happen than to happen.

  • Even chance: one thing is not more likely to happen than the other

  • Likely: more likely to happen than not to happen.

Order and compare likelihood

This video is about describing and ordering the likelihood of events.

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Examples

Example 3

The events A, B, C and D have probabilities as shown on this probability line:

A probability line showing Impossible, Even chance, certain and events A, B, C, D. Ask your teacher for more information.
a

Which events are more likely to occur than event B?

A
Events A and C
B
Events C and D
C
Events A and D
Worked Solution
Create a strategy

Find which events are to the right of event B.

Apply the idea

The events that are further to the right on the scale than event B are events C and D. So the correct answer is Option B.

b

Which events are less likely to occur than event C?

A
Events A and B
B
Events B and D
C
Events A and D
Worked Solution
Create a strategy

Find which events are to the left of event C.

Apply the idea

The events that are further to the left on the scale than event C is event A and B. So the correct answer is option A.

Idea summary

To think about the order of events being likely or not, it may help to start with something that will definitely happen (certain) or definitely won't happen (impossible).

In order of how much chance something has of happening, we can start from the left, and move right. It's just like a number line.

An arrow going to the right to show the order of chances from impossible, unlikely, even, likely, to certain.

Outcomes

MA3-19SP

conducts chance experiments and assigns probabilities as values between 0 and 1 to describe their outcomes

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