2. OBJECTIVE
To find the probability of compound events,
using the addition rules.
3. MUTUALLY EXCLUSIVE EVENTS
Two events are mutually exclusive if they
cannot occur at the same time (i.e., they
have no outcomes in common).
4. ADDITION RULE 1
When two events A and B are mutually
exclusive, the probability that A or B will
occur is P(A or B) = P(A) + P(B)
5. ADDITION RULE 2
If A and B are not mutually exclusive events,
then P(A or B) = P(A) + P(B) – P(A and B).
6. EXAMPLE
Mutually exclusive or not?
Getting a 7 and getting a jack
Getting a club and getting a king
Getting a face card and getting an ace
Getting a face card and getting a spade
7. EXAMPLE
A box contains 3 glazed doughnuts, 4 jelly
doughnuts, and 5 chocolate doughnuts. If a
person selects a doughnut at random, find
the probability that it is either a glazed
doughnut or a chocolate doughnut.
8/12 or 2/3 or 66.7%
8. EXAMPLE
At a political rally, there are 20 Republicans,
13 Democrats, and 6 Independents. If a
person is selected at random, find the
probability that he or she is either a
Democrat or an Independent.
19/39 or 48.7%
9. EXAMPLE
A day of the week is selected at random.
Find the probability that it is a weekend day.
2/7 or 28.6%
10. EXAMPLE
A single card is drawn from a deck. Find the
probability that it is a king or a club.
16/52 or 4/13 or 30.8%
11. EXAMPLE
In a hospital unit there are 8 nurses and 5
physicians; 7 nurses and 3 physicians are
females. If a staff person is selected, find the
probability that the subject is a nurse or a
male.
10/13 or 76.9%
12. EXAMPLE
On New Year’s Eve, the probability of a
person driving while intoxicated is 0.32, the
probability of a person having a driving
accident is 0.09, and the probability of a
person having a driving accident while
intoxicated is 0.06. What is the probability of
a person driving while intoxicated or having a
driving accident?
35%
13. THREE EVENTS
Mutually Exclusive:
P(A or B or C) = P(A) + P(B) + P(C)
Not Mutually Exclusive:
P(A or B or C) = P(A) + P(B) + P(C) – P(A and B) –
P(B and C) – P(A and C) + P(A and B and C)
