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The probability scale

I can assign a numerical value to an outcome to give the probability that the outcome will occur.

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Year 9

The probability scale

I can assign a numerical value to an outcome to give the probability that the outcome will occur.

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Lesson details

Key learning points

Probability is a measure of the likelihood of an outcome happening.
An outcome can be assigned a numerical value from 0 to 1
The probability scales shows the numerical values that an outcome might have.

Keywords

Probability - The probability that an event will occur is the proportion of times the event is expected to happen in a suitably large experiment.

Common misconception

Pupils think that 'likely' from the scale of likelihoods is only equal to a specific probability (e.g. 75%).

All probabilities that are greater than 50% but less than 100% are equivalent to 'likely' on the scale of likelihoods.

Question 4 in Task B contains a link to a Desmos file. If pupils have access to a web browser, they could use to link to simulate an experiment. If pupils do not have access to a web browser then the teacher could display the simulation on the screen or run it in advance and print off the results.

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Licence

This content is © Oak National Academy Limited (2026), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Prior knowledge starter quiz

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6 Questions

Q1.
Which letter on the scale of likelihoods represents 'even chance'?

Correct answer: C

Q2.
What does the letter A represent on the scale of likelihoods?

certain

even chance

Correct answer: impossible

likely

unlikely

Q3.
Which word describes the likelihood of an outcome that is guaranteed to happen?

Correct answer: certain

even chance

impossible

likely

unlikely

Q4.
Which percentage is equivalent to 0.1?

0.001%

0.01%

0.1%

Correct answer: 10%

Q5.
Which fraction is equivalent to 50%?

Correct answer: $${1}\over{2}$$

$${1}\over{5}$$

$${1}\over{20}$$

$${1}\over{50}$$

Q6.
What is 25% of 2000?

Correct Answer: 500, five hundred

Assessment exit quiz

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6 Questions

Q1.
The letter E on the scale represents a probability of %.

Correct Answer: 100

Q2.
Which probabilities are equivalent to an 'even chance'?

0.2

Correct answer: $${1}\over{2}$$

Correct answer: 0.5

Correct answer: 50%

$${1}\over{5}$$

Q3.
What is the probability of an event that is impossible?

Correct Answer: 0, 0%, zero, 0 percent, zero percent

Q4.
Which is the probability that this spinner lands on 'win'?

Correct answer: 47%

50%

53%

99%

Q5.
A trial has three possible outcomes: {A, B, C}. P(A) = $${1}\over{2}$$. P(B) = $${1}\over{3}$$. P(C) = $${1}\over{6}$$. Which outcome is most likely to happen?

Correct answer: A

Q6.
The probability on an outcome is 20%. Approximately how many times could you expect the outcome to occur in 500 trials?

Correct answer: 100

200

250

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UnitMaths / Probability: theoretical probabilities

Maths

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The probability scale

The probability scale

Lesson slides

Lesson details

Key learning points

Keywords

Common misconception

Licence

Lesson video

Worksheet

Prior knowledge starter quiz

6 Questions

Q1.Which letter on the scale of likelihoods represents 'even chance'?

Q2.What does the letter A represent on the scale of likelihoods?

Q3.Which word describes the likelihood of an outcome that is guaranteed to happen?

Q4.Which percentage is equivalent to 0.1?

Q5.Which fraction is equivalent to 50%?

Q6.What is 25% of 2000?

Assessment exit quiz

6 Questions

Q1.The letter E on the scale represents a probability of %.

Q2.Which probabilities are equivalent to an 'even chance'?

Q3.What is the probability of an event that is impossible?

Q4.Which is the probability that this spinner lands on 'win'?

Q5.A trial has three possible outcomes: {A, B, C}. P(A) = $${1}\over{2}$$. P(B) = $${1}\over{3}$$. P(C) = $${1}\over{6}$$. Which outcome is most likely to happen?

Q6.The probability on an outcome is 20%. Approximately how many times could you expect the outcome to occur in 500 trials?

Lesson appears in

UnitMaths / Probability: theoretical probabilities

Maths

Q1.
Which letter on the scale of likelihoods represents 'even chance'?

Q2.
What does the letter A represent on the scale of likelihoods?

Q3.
Which word describes the likelihood of an outcome that is guaranteed to happen?

Q4.
Which percentage is equivalent to 0.1?

Q5.
Which fraction is equivalent to 50%?

Q6.
What is 25% of 2000?

Q1.
The letter E on the scale represents a probability of %.

Q2.
Which probabilities are equivalent to an 'even chance'?

Q3.
What is the probability of an event that is impossible?

Q4.
Which is the probability that this spinner lands on 'win'?

Q5.
A trial has three possible outcomes: {A, B, C}. P(A) = $${1}\over{2}$$. P(B) = $${1}\over{3}$$. P(C) = $${1}\over{6}$$. Which outcome is most likely to happen?

Q6.
The probability on an outcome is 20%. Approximately how many times could you expect the outcome to occur in 500 trials?