Download Addition & Multiplication Rules

Addition & Multiplication Rules
BUSA 2100, Section 4.3
Special Addition Rule
Example 1: In Lowndes County, 25% of
the cars owned were made by GM and
20% were made by Ford.
 What is the probability that a randomly
chosen car was made by GM or Ford?

Special Addition Rule, p. 2

Draw a Venn diagram for Example 1.

Can be extended to more than 2 events.
General Addition Rule
Ex. 2: Among junior VSU Business
majors, 35% are taking BUSA 2100 this
term, and 45% are taking MGNT 3250.
 What is the probability that a junior
Business student is taking Statistics or
Management?
 Can we just add the probabilities?
Draw a Venn diagram.

General Addition Rule, Page 2

If in doubt, use the General Add. Rule.
Independent and Dependent
Events
Definition: Two events are independent
if the occurrence of one event has no
effect on whether or not the other event
occurs.
 Two events are dependent if the occurrence of one event has some effect on
whether or not the other event occurs.

Independent and Dependent
Events, Page 2
If 2 events are dep., it doesn’t mean 1
event causes or requires the other.
 Dependence means the occurrence of 1
event affects (increases, decreases)
the probability that the other will occur.
 Ex. 1: A = “family with annual income >
$100,000”; B = “family with luxury car <
2 years old”. Are A, B indep. or dep.?

Independent and Dependent
Events, Page 3
Example 2: C = “man with a shoe size >
10”; D = “man with IQ > 115”. Are C, D
independent or dependent? Why?
 Example 1: A coin is flipped and a die
is rolled. What is the probability of a
head on the coin and a six on the die?

Special Multiplication Rule
Special Multiplication Rule,
Page 2
Example 2: At a gas station, 70% of the
customers use credit cards.
 For the next 2 customers, what is the
probability that the 1st one uses a credit
card and the 2nd one does not?
