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Objective
Find the probability of a simple event
Vocabulary
Outcome
One possible result of a probability event
Vocabulary
Sample space
The set of all possible outcomes of a
probability experiment
Vocabulary
Random
Outcomes occur at random if each outcome is
equally likely to occur
Vocabulary
Simple event
A specific outcome or type of outcome
Vocabulary
Probability
The chance that some event will happen
Vocabulary
Complementary events
The events of one outcome happening and that
outcome not happening are complementary
events
Example 1 Find Probabilities
Example 2 Find Probabilities
Example 3 Find Probabilities
Example 4 Probability of a Complementary Event
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is yellow?
Write probability statement
Numerator is in probability
statement
Denominator is “total
numbers possible”
1/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is yellow?
P(yellow) =
Replace “yellow marbles”
with 10
Answer:
P(yellow) =
Count total marbles
5 + 10 + 10 = 25
Simplify fraction with
calculator
1/4
A bag contains 3 green marbles, 7 purple marbles,
and 15 black marbles. A marble is picked at random.
What is the probability the marble is black?
Answer: P(black) =
1/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is blue or red?
red
Write probability statement
Numerator is in probability
statement
Denominator is “total
numbers possible”
2/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is blue or red?
red
P(blue or red) =
Replace “blue marbles” with 5
Replace “red marbles” with 10
Count total marbles
5 + 10 + 10 = 25
2/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is blue or red?
red
P(blue or red) =
Follow Order of Operations
P
E
MD
AS
P(blue or red) =
Add numerator
Bring down denominator
2/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
What is the probability the marble is blue or red?
red
P(blue or red) =
Simplify fraction with
calculator
P(blue or red) =
Answer:
P(blue or red) =
2/4
A bag contains 3 green marbles, 7 purple marbles,
and 15 black marbles. A marble is picked at random.
What is the probability the marble is green or purple?
Answer:
P(green or purple) =
2/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
white
What is the probability the marble is white?
P(white) =
White Marbles
Total Number of Marbles
Write probability statement
Numerator is in probability
statement
Denominator is “total
numbers possible”
3/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
white
What is the probability the marble is white?
White Marbles
P(white) =
Total Number of Marbles
P(white) = 0
25
Replace “white marbles” with
0 since there are no white
marbles
Count total marbles
5 + 10 + 10 = 25
3/4
A bag contains 5 blue marbles, 10 red marbles, and
10 yellow marbles. A marble is picked at random.
white
What is the probability the marble is white?
White Marbles
P(white) =
Total Number of Marbles
P(white) = 0
25
Simplify fraction with
calculator
Answer:
P(white) = 0
3/4
A bag contains 3 green marbles, 7 purple marbles,
and 15 black marbles. A marble is picked at random.
What is the probability the marble is red?
Answer: P(red) = 0
3/4
PHONE LISTINGS One town has 10,000 phone
numbers in use. Of these, 500 are not listed in the local
phone book. What is the probability that the phone
number you are looking for is listed in the phone book?
book
Write probability statement
Numerator is in probability
statement
Denominator is “total
numbers possible”
4/4
PHONE LISTINGS One town has 10,000 phone
numbers in use. Of these, 500 are not listed in the local
phone book. What is the probability that the phone
number you are looking for is listed in the phone book?
book
P(listed) =
Given 500 not listed
Must subtract from total
numbers to find listed
numbers
10,000 - 500 = 9,500
4/4
PHONE LISTINGS One town has 10,000 phone
numbers in use. Of these, 500 are not listed in the local
phone book. What is the probability that the phone
number you are looking for is listed in the phone book?
book
P(listed) =
Total phone numbers is
10,000
4/4
PHONE LISTINGS One town has 10,000 phone
numbers in use. Of these, 500 are not listed in the local
phone book. What is the probability that the phone
number you are looking for is listed in the phone book?
book
P(listed) =
95
P(listed) =
100
Since large fractions do not
work in calculator, cancel out
2 zeros in numerator and
denominator
4/4
PHONE LISTINGS One town has 10,000 phone
numbers in use. Of these, 500 are not listed in the local
phone book. What is the probability that the phone
number you are looking for is listed in the phone book?
book
95
P(listed) =
100
Simplify using a calculator
Answer:
P(listed) =
4/4
*
SCHOOL ATTENDANCE Oakdale Junior High School
has a total enrollment of 670 students. Of these, 45 are
absent today. Suppose a student’s name is picked at
random. What is the probability that the student picked
is absent today?
Answer: P(student absent) =
4/4
Assignment
Lesson 8:1 Probability of Simple Events
4 - 21 All