Basic probability: GCSE Maths revision
Probability is a number from 0 to 1. For equally likely outcomes, P(event) = favourable ÷ total.
The scale
0 is impossible, 1 is certain. Probabilities of all mutually exclusive outcomes of a trial sum to 1.
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
A fair six-sided dice. P(even)?
A spinner has 3 red and 5 blue. P(red)?
P(rain) = 0.3. P(not rain)?
Common mistakes
- Writing probabilities as ratios instead of fractions, decimals or percentages as asked.
- Forgetting outcomes must be equally likely for the simple formula.
Answers and working
Frequently asked questions
Can probability be 1.2?
No. A single event cannot have probability greater than 1.
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