Mathematics·Statistics and probability · NSSCO 12.4
Probability
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Probability is the maths of how likely things are, and this lesson builds it up gently from scratch. We start with the probability scale from 0 to 1, learn to work out the probability of a single event, and the neat 'not' rule. Then we try experimental probability and expected frequency, combine two events with sample-space grids, meet the OR rule and the AND rule, and finish with tree diagrams — both with and without replacement.
What you'll learn in this lesson
By the end you should be able to (NSSCO Mathematics 12.4):
- Use the probability scale from 0 (impossible) to 1 (certain)
- Calculate the probability of a single event as favourable outcomes ÷ total outcomes (a fraction or decimal, not a ratio)
- Use the complement: P(not A) = 1 − P(A)
- Find experimental probability (relative frequency) from trials
- Calculate expected frequency as probability × number of trials
- List combined outcomes using a possibility (sample) space diagram
- Add probabilities for mutually exclusive events (the OR rule)
- Multiply probabilities for independent events (the AND rule)
- Use tree diagrams to solve problems, with and without replacement
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