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Lesson 2 of 13

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 2 of 13
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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.

Lesson details

Key learning points

  1. Probability is a measure of the likelihood of an outcome happening.
  2. An outcome can be assigned a numerical value from 0 to 1
  3. 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.
Teacher tip

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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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'?

An image in a quiz
A
B
Correct answer: C
D
E

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

An image in a quiz
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%
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 %.

An image in a quiz
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'?

An image in a quiz
1%
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
B
C

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

20
50
Correct answer: 100
200
250

Lesson appears in

UnitMaths / Probability: theoretical probabilities

Maths

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