Probability | A-Level Maths

What does P(A) mean?

P(A) is the probability of A happening

What does P(A') mean?

P(A') is the probability of A not happening

What does P(A∩B) mean?

P(A∩B) is the probability of A and B happening

What does P(AUB) mean?

P(AUB) is the probability of only A happening, or only B happening, or both A and B happening

What does P(A|B) mean?

P(A|B) is the probability of A happening given that we know B is also happening.

What does independent mean?

A and B are independent if P(A∩B) = P(A) x P(B)

What does mutually exclusive mean?

A and B are mutually exclusive if P(A∩B) = 0

Venn Diagrams

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Conditional Probability in Venn Diagrams

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Probability Tree Diagrams

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Conditional Probability in Tree Diagrams

What is the formula for P(A|B)?

P(A|B) = P(A∩B)/P(B)

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