GCSE MATHS • HIGHER TIER
Probability Scale Made Simple
Describe likelihood, place probabilities from 0 to 1 and interpret chance confidently.
Clear method
Exam practice
Worked proofs
Probability Scale in Four Moves
1
Identify
Identify the event and its probability.
2
Position
Place the probability between 0 and 1.
3
Describe
Use words such as impossible, unlikely, even chance, likely or certain.
4
Check
Make sure the probability lies between 0 and 1 and matches the event.
What You’ll Learn
Understand what the probability scale represents.
Recognise the key values 0, 0.5 and 1.
Understand impossible, certain and even-chance events.
Calculate probabilities and position them on the scale.
Describe probabilities using appropriate words.
Apply the probability scale to real-life situations.
Key Rules
The probability scale runs from 0 to 1.
0 means the event is impossible.
0.5 means the event has an even chance.
1 means the event is certain.
Values below 0.5 represent unlikely events.
Worked Proof: Probability Scale
Step-by-Step Method
- 1. Identify the event and its probability.
- 2. Convert the probability to a decimal if needed.
- 3. Place the value between 0 and 1 on the scale.
- 4. Describe it as impossible, unlikely, even chance, likely or certain.
- 5. Check that the position and description match the event.
More Worked Examples
1
Question: What is the probability of rolling a 3 on a fair dice?
There is 1 favourable outcome and 6 possible outcomes.
Probability = 1/6 ≈ 0.17
2
Question: What is the probability of getting heads on a fair coin?
Probability = 1/2 = 0.5
3
Question: A bag contains 8 red balls and 2 blue balls. Find the probability of selecting a blue ball.
Probability = 2/10 = 0.2
4
Question: A spinner has 10 equal sections and 7 are green.
Probability = 7/10 = 0.7
- Common GCSE Mistakes
- Confusing impossible events with unlikely events.
- Forgetting that probabilities must be between 0 and 1.
- Placing probabilities incorrectly on the scale.
- Misinterpreting fractions and decimals.
- Exam Tips
- Remember the three key benchmarks: 0, 0.5 and 1.
- Convert fractions to decimals when this makes placement on the scale easier.
- Check that every probability lies between 0 and 1.
- Use the event description to judge whether your calculated value is sensible.
- Distinguish carefully between impossible and merely unlikely.
- Practise matching numerical probabilities to words such as likely and even chance.
Skills Used in Probability Scale
Probability
Fractions
Decimals
Percentages
Likelihood
Interpreting Scales
Comparing Values
Problem Solving
Ready to Practise?
Printable Worksheet
Download and print practice questions with answers.
Interactive Quiz
Test your knowledge with instant feedback and hints.
Exam-Style Questions
Timed questions to build confidence for the real exam.
Watch the Probability Scale Tutorial
Step-by-step walkthroughs of Probability Scale with clear methods and exam tips.
Frequently Asked Questions
It is a line from 0 to 1 that shows how likely an event is to occur.
A probability of 0 means the event is impossible.
A probability of 1 means the event is certain.
A probability of 0.5 represents an even chance.
No. The source states that probabilities must always be between 0 and 1.
Use descriptions such as impossible, unlikely, even chance, likely and certain according to where the probability lies on the scale.