Suppose S and T are mutually exclusive events. Find P(S or T) if P(S) = 1/3 and P(T) = 5/12?

3/4
7/18
5/36

2 Answers
Apr 20, 2017

In an OR situation you may ADD

Explanation:

P(SorT)=P(S)+P(T)=13+512=412+512=912=34

Apr 24, 2017

P(ST)=34

Explanation:

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

P(AB)=P(A)+P(B)P(AB)

And if we apply this to our problem we have:

P(ST)=P(S)+P(T)P(ST)
=13+512P(ST)
=34P(ST)

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

P(ST)=0

Hence,

P(ST)=34