probability of exactly two out of three events occuring

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Given that we have three disjoint events, a,b,c and their probabilities are given as P(A), P(B), P(A ∪ B) etc, how can we find the probability of only two by three events occurring at one point?

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Your answer has assumed that $A,B$ and $C$ are independent.

A more general formula would be $$p(A\cap B)+p(B\cap C)+p(C\cap B)-3p(A\cap B\cap C).$$

EXAMPLE

Consider throwing a die. Let $A$ be the event of getting a $6$, $B$ the event of getting a $5$ and $C$ the event of getting at least $5$.

The the probability of precisely two events occurring is $\frac{1}{3}$ whereas your formula gives $\frac{1}{9}$.