# Math Help - mutually exclusive events

1. ## mutually exclusive events

So, two mutually exclusive events A and B

P(A or B)=P(A)+P(B).

But what if the probabilities add up to be greater than 1? We can't subtract P(AandB).

Can P(A or B) with mutually exclusive events be greater than 1?

2. Originally Posted by sfspitfire23
So, two mutually exclusive events A and B
P(A or B)=P(A)+P(B).
But what if the probabilities add up to be greater than 1? We can't subtract P(AandB).

Can P(A or B) with mutually exclusive events be greater than 1?
The answer is no. Not in the same probability space

3. So, if P(A)=.9 and P(B)=.9 and the events are mutually exclusive, what is P(A or B)?

4. Originally Posted by sfspitfire23
So, if P(A)=.9 and P(B)=.9 and the events are mutually exclusive, what is P(A or B)?
The point is the bit above is impossible. It cannot happen.
Consider, $P(A \cup B) = P(A) + P(B) - P(A \cap B) \leqslant 1$.
From the given $P(A \cap B) \geqslant 0.8$.
Because $P(A \cap B) \ne 0$ the events are not mutually exclusive.