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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?

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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) =

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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

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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) =

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Assignment

Lesson 8:1 Probability of Simple Events 4 - 21 All