Question

Suppose S and T are mutually exclusive events. Find P(S or T) if P(S) = 65% and P(T) = 7%.

Answer 1

P(S∪T)=34

Explanation:

We use the following fundamental definition from Probability and Set Theory:

P(A∪B)=P(A)+P(B)−P(A∩B)

And if we apply this to our problem we have:

P(S∪T)=P(S)+P(T)−P(S∩T)
=13+512−P(S∩T)
=34−P(S∩T)

Now we are told that S and T are mutually exclusive, and so:

P(S∩T)=0

Hence,

P(S∪T)=34