# Probability: mutually exclusive events

• Oct 1st 2008, 09:55 AM
sohalia34
Probability: mutually exclusive events
Hi!
So i don't know why but i am totally bugging on this problem:

"An experiment results in one of three mutually exclusive events A,B and C. It is knows that p(A)=.30, p(B)=.55 and p(C)=.15.
Find each of the following probabilities:
a - p(a u b)
b - p(a n b)
c - p(a|b)
d - p(b u c) "

so i would know how to find b-, c- and d- but i can't get started with a-.

they say it's mutually exclusive, but does it mean that p(a n b n c)=0 or that p(a n b)= 0 and p(a n c)=0 and p(b n c)= 0 ?

I am confused! Thanks..
• Oct 1st 2008, 10:26 AM
Plato
Quote:

Originally Posted by sohalia34
An experiment results in one of three mutually exclusive events A,B and C. It is knows that p(A)=.30, p(B)=.55 and p(C)=.15.
Find each of the following probabilities:
a - p(a u b) b - p(a n b) c - p(a|b) d - p(b u c) "

they say it's mutually exclusive, but does it mean that p(a n b n c)=0 or that p(a n b)= 0 and p(a n c)=0 and p(b n c)= 0 ?

The term mutually exclusive usually means pairwise disjoint.
So yes, the above would all be zero.
$\displaystyle \begin{array}{rcl} {P(A \cup B)} & = & {P(A) + P(B) - P(A \cap B)} \\ {} & = & {P(A) + P(B) - P(\emptyset )} \\ {} & = & {P(A) + P(B)} \\ \end{array}$