11-1 Introduction to Probability
Learn to estimate the likelihood of an
event and to write and compare
probabilities.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Vocabulary
probability
Course 1
11-1 Introduction to Probability
Probability is the measure of how likely
an event is to occur.
Course 1
11-1 Introduction to Probability
Probabilities are written as fractions or decimals
from 0 to 1 or as percents from 0% to 100%. The
higher an event’s probability, the more likely that
event is to happen.
• Events with a probability of 0, or 0%, never
happen.
• Events with a probability of 1, or 100%, always
happen.
• Events with a probability of 0.5, or 50%, have the
same chance of happening as of not happening.
Course 1
11-1 Introduction to Probability
Impossible
0
0%
Unlikely As likely as not
0.5
1
__
2
50%
Course 1
Likely
Certain
1
100%
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 1A & 1B: Estimating the
Likelihood of an Event
Write impossible, unlikely, as likely as not,
likely, or certain to describe each event.
A. You will roll an even number on a standard
number cube.
as likely as not
B. The month of February has 28 days.
certain
Helpful Hint
A standard number cube is numbered from 1 to 6.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 1C & 1D: Estimating the
Likelihood of an Event
Write impossible, unlikely, as likely as not,
likely, or certain to describe each event.
C. This spinner lands on blue.
unlikely
D. This spinner lands on an odd number.
impossible
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 1A & 1B
Write impossible, unlikely, as likely as not,
likely, or certain to describe each event.
A. You guess a number between 1 and 1000.
unlikely
B. You will roll an odd number on a standard
number cube.
as likely as not
Helpful Hint
A standard number cube is numbered from 1 to 6.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 1C & 1D
Write impossible, unlikely, as likely as not,
likely, or certain to describe each event.
C. This spinner lands on green.
unlikely
D. This spinner lands on an even number.
certain
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 2A & 2B: Writing Probabilities
A. The weather report gives a 75% chance of
snow. Write this probability as a decimal and as a
fraction.
75% = 0.75
Write as a decimal.
75
3
Write as a fraction in
75% = ___ = __
simplest form.
100
4
B. The chance of being chosen is 0.8. Write
this probability as a fraction and as a percent.
8
4
__
__
0.8 =
=
10
5
0.8 = 80%
Course 1
Write as a fraction in
simplest form.
Write as a percent.
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 2C: Writing Probabilities
7
__
C. There is a
chance of getting a ring. Write
50
this probability as a decimal and as a percent.
7
__
= 7 ÷ 50 = 0.14
50
Write as a decimal.
7
7•2
14
__
= _____ = ___ = 14%
50 50 • 2
100
Write as a percent.
Helpful Hint
In Example 2C, after you find the decimal form
7 , you can use it to find the percent.
of __
50
0.14 = 14%.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 2A & 2B
A. The weather report gives a 25% chance of
snow. Write this probability as a decimal and as
a fraction.
25% = 0.25
Write as a decimal.
25
1
Write as a fraction in
25% = ___ = __
simplest form.
100
4
B. The chance of being chosen is 0.6. Write
this probability as a fraction and as a percent.
6
3
__
__
0.6 =
=
10
5
0.6 = 60%
Course 1
Write as a fraction in
simplest form.
Write as a percent.
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 2C
4
__
C. There is a
chance of getting a ring. Write
25
this probability as a decimal and as a percent.
4
__
= 4 ÷ 25 = 0.16
25
Write as a decimal.
4
4•4
16
__
= _____ = ___ = 16%
25 25 • 4
100
Write as a percent.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 3A: Comparing Probabilities
A. On a standard number cube, there is a 50%
1
__
chance of rolling a multiple of 2 and a 33
%
3
chance of rolling a multiple of 3. Is it more
likely to roll a multiple of 2 or a multiple of 3?
1
Compare: 33 __% < 50%
3
It is more likely to roll a multiple of 2.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Additional Example 3B: Comparing Probabilities
B. When you spin a certain spinner, there is a
15% chance that it will land on yellow, a 15%
chance it will land on green, and a 70% chance
that it will land on purple. Is it more likely to
land on purple or on green?
Compare: 70% > 15%
It is more likely to land on purple than on green.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 3A
A. When you spin a certain spinner, there is a
25% chance that it will land on purple, a 35%
chance it will land on green, and a 40% chance
that it will land on red. Is it more likely to land
on red or on green?
Compare: 40% > 35%
It is more likely to land on red than on green.
Course 1
11-1 Introduction
Insert Lesson
Here
toTitle
Probability
Try This: Example 3B
B. When you spin a certain spinner, there is a
1
9% chance that it will land on yellow, a 35 __ %
3
2 %
chance it will land on brown, and a 55 __
3
chance that it will land on blue. Is it more likely
to land on brown or on yellow?
1
__
Compare: 9% < 35
%
3
It is more likely to land on brown than on yellow.
Course 1
11-1 Introduction
Insert Lesson
toTitle
Probability
Here
Lesson Quiz
Write impossible, unlikely, equally likely,
likely, or certain to describe each event.
1. The sun will rise tomorrow. certain
2. You will roll 13 when rolling two dice. impossible
3. There is a 0.125 chance of picking the winning
ticket. Write this probability as a fraction and as a
1 , 12.5%
percent. __
8
4. At Hamburger Hut, there is a 20% chance of
getting a plastic dinosaur cup and a 35% chance of
getting a plastic rabbit cup. It is less likely that you
will receive a rabbit cup or dinosaur cup?
dinosaur cup
Course 1