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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?
1/4
Write probability statement
What is the probability the marble is yellow?
Numerator is in probability statement
Denominator is “total numbers possible”
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?
1/4
What is the probability the marble is yellow?
Replace “yellow marbles” with 10
P(yellow) =
Count total marbles
5 + 10 + 10 = 25
Simplify fraction with calculator
P(yellow) =Answer:
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?
2/4
Write probability statement
What is the probability the marble is blue or red
Numerator is in probability statement
Denominator is “total numbers possible”
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?
2/4
What is the probability the marble is blue or red
Replace “blue marbles” with 5P(blue or red) =
Replace “red marbles” with 10
Count total marbles
5 + 10 + 10 =25
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?
2/4
What is the probability the marble is blue or red
Follow Order of Operations
P E MD AS
P(blue or red) =
Add numeratorP(blue or red) =
Bring down denominator
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?
2/4
What is the probability the marble is blue or red
P(blue or red) =
P(blue or red) =
Simplify fraction with calculator
P(blue or red) =Answer:
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. What is the probability the marble is white?
P(white) = White Marbles
Total Number of Marbles
3/4
Write probability statement
What is the probability the marble is white
Numerator is in probability statement
Denominator is “total numbers possible”
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 white?
P(white) = White Marbles
Total Number of Marbles
3/4
What is the probability the marble is white
Replace “white marbles” with 0 since there are no white marbles
P(white) = 0
Count total marbles
5 + 10 + 10 =25
25
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 white?
P(white) = White Marbles
Total Number of Marbles
3/4
What is the probability the marble is white
P(white) = 025
Simplify fraction with calculator
P(white) = 0 Answer:
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?
4/4
Write probability statement
What is the probability that the phone number you are looking for is listed in the phone book
Numerator is in probability statement
Denominator is “total numbers possible”
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?
4/4
What is the probability that the phone number you are looking for is listed in the phone book
Given 500 not listed
Must subtract from total numbers to find listed numbers
10,000 - 500 = 9,500
P(listed) =
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?
4/4
What is the probability that the phone number you are looking for is listed in the phone book
P(listed) = Total phone numbers is 10,000
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?
4/4
What is the probability that the phone number you are looking for is listed in the phone book
P(listed) = Since large fractions do not work in calculator, cancel out 2 zeros in numerator and denominatorP(listed) = 95
100
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?
4/4
What is the probability that the phone number you are looking for is listed in the phone book
Simplify using a calculatorP(listed) = 95
100
P(listed) = Answer:
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
