Probability Models and Counting
Ages 16–18Difficulty adapts to you
Probability Models and Counting
For equally likely outcomes, probability is favourable outcomes divided by total outcomes. A sample space lists every possible result. Use organised tables, tree diagrams, or counting rules to avoid missing or repeating outcomes.
Your goals
- ✓You can list outcomes, calculate probabilities, and use sample spaces without double-counting.
- ✓You can use Probability Models and Counting, model correctly.
- ✓You can use the definitions, units, assumptions, and examples to check your answer.
Words to know
- Probability Models and Counting:
- List outcomes, calculate probabilities, and use sample spaces without double-counting.
- model:
- A rule or representation used to describe a situation and make a prediction.
Examples
- 1The probability of rolling an even number on a fair die is 3 ÷ 6 = 1/2.
- 2Two coin tosses have HH, HT, TH, TT; exactly one head has probability 2/4 = 1/2.
Check these
- • Do not skip the meaning of a term or give a result without explaining what it means.
- • Keep every number, symbol, label, and unit in its correct place.
- • Show enough working to check how you reached your answer.
Helpful habits
- • Read the whole question before choosing what to do.
- • Show one clear step at a time and check each step.
- • If you are stuck, draw a model, try smaller numbers, or revisit the example.
Now try your own
Create your own probability models and counting example, solve it, and explain how you checked it.
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