Combined events: GCSE Maths revision
For mutually exclusive events, P(A or B) = P(A) + P(B). For independent events, P(A and B) = P(A) × P(B).
Mutually exclusive vs independent
Mutually exclusive: cannot happen together (a 6 and a 5 on one roll). Independent: one does not affect the other (two separate dice).
Try these questions
Cover the answers and have a go first. Worked solutions are underneath.
Fair dice. P(2 or 5)?
Two coins. P(H and H)?
Common mistakes
- Adding independent “and” probabilities.
- Using P(A) + P(B) when A and B can both happen (then you must subtract the overlap).
Answers and working
Frequently asked questions
What if events are not mutually exclusive?
P(A or B) = P(A) + P(B) − P(A and B).
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