Probability
Maths, Statistics. Usually met in years 7 to 11.
Work out simple probabilities, probabilities of not happening, combined events and expected outcomes.
What you practise
- Simple probability
- Independent events
- Without replacement
Ends with two events taken without replacement. Practice moves up a level when a round goes well and down when it does not.
Sample questions
Each sample comes with the method and the reason every wrong option is wrong. Real practice rounds are ten questions at your level.
Sample question, level 2 of 5
The probability that it rains on sports day is 0.28. What is the probability that it does not rain?
- 1.28
- 0.82
- 0.72
- 72
- 0.28
Show the answer and method
Answer: C, 0.72
The method: The probability of something happening and the probability of it not happening add up to 1, so 1 − 0.28 = 0.72.
Why the other options are wrong:
- A, 1.28: The probability was added to 1. Probabilities of an event and its opposite add to 1, so subtract.
- B, 0.82: Close, but check the subtraction.
- D, 72: A probability is between 0 and 1: this looks like a percentage.
- E, 0.28: This is the probability that it rains on sports day.
Sample question, level 4 of 5
The probability that a player scores from a free throw is 0.8. Roughly how many of 500 free throws would you expect them to score?
- 40
- 4000
- 100
- 625
- 400
Show the answer and method
Answer: E, 400
The method: Expected number = probability × number of trials = 0.8 × 500 = 400.
Why the other options are wrong:
- A, 40: The decimal point is one place out.
- B, 4000: The decimal point is one place out.
- C, 100: This is the number you would expect not to happen.
- D, 625: The number of trials was divided by the probability.
See where this fits: GCSE maths with AQA and Key Stage 3.
Related topics: Averages.
