Probability · Year 7
In Year 7 you learn: probabilities as fractions.
Probability measures how likely something is, on a scale from 0 (impossible) to 1 (certain). You can work it out from equally likely outcomes. Or you can estimate it from an experiment, using relative frequency.
Key facts
- P(not A) = 1 − P(A).
- Expected frequency = probability × number of trials.
- Mutually exclusive events: P(A or B) = P(A) + P(B).
- Independent events: P(A and B) = P(A) × P(B).
Worked examples
Example 1
A bus is early with probability 0.15 and on time with probability 0.6. Find P(late), and how many late days to expect in 40 school days.
Answer: 0.25; 10 days