Page 1 of 5
Percents and Decimals
BEFORE
Now
You wrote percents as fractions
and fractions as percents.
You’ll write percents as decimals So you can find the price of a
and decimals as percents.
vintage toy, as in Ex. 18.
WHY?
In the Real World
Word Watch
Review Words
decimal, p. 52
percent, p. 415
Geography The surface area of Lake
Tarpon is 0.5% of the surface area of
Lake Okeechobee. The surface area of
Lake Weohyakapka is 300% of the surface
area of Lake Tarpon. How can you write
these percents as decimals? You’ll find the
answer in Example 4.
FLORIDA
Lake
Tarpon
You can write a percent as a decimal and
a decimal as a percent by using a fraction
as an intermediate step. For example:
Lake
Weohyakapka
Lake
Okeechobee
37
100
37% 37 100 0.37
So, 37% 0.37. Notice that 37% can be written as a decimal by dropping
the percent sign and moving the decimal point two places to the left.
Similarly, a decimal can be written as a percent by moving the decimal
point two places to the right and adding a percent sign.
1
EXAMPLE
Writing Percents as Decimals
a. 48% 48%
b. 9% 09%
0.48
0.09
2
EXAMPLE
a. 0.13 .13
0.755
Writing Decimals as Percents
b. 0.04 .04
c. 0.027 .027
4%
2.7%
13%
Your turn now
a percent.
c. 75.5% 75.5%
Write the percent as a decimal or the decimal as
1. 25%
2. 1%
3. 5.2%
4. 0.082
5. 0.06
6. 0.578
Lesson 9.3
Percents and Decimals
425
Page 2 of 5
You can write a fraction as a percent by writing the fraction as a decimal
and then moving the decimal point two places to the right.
EXAMPLE
with
Reading
The symbol ≈ is read “is
approximately equal to.” It
indicates that a result has
been rounded and is not
exact.
3
a. 5 ≈ 0.833
6
83.3%
3
b. 7 ≈ 0.429
42.9%
Writing Fractions as Percents
Write as a decimal rounded
to the nearest thousandth.
Write as a percent.
Write as a decimal rounded
to the nearest thousandth.
Write as a percent.
Small and Large Percents Percents less than 1% represent numbers
1
100
that are less than 0.01, or . Percents greater than 100% represent
numbers that are greater than 1. For example, the models below
represent 0.5% and 150%, respectively.
EXAMPLE
4
Rewriting Small and Large Percents
To write the percents discussed on page 425 as decimals, follow the same
rules as for percents between 1% and 100%.
Lake Tarpon: 0.5% 00.5%
Lake Weohyakapka: 300% 300%
0.005
3
Your turn now
Write the fraction as a percent. Round to the nearest
tenth of a percent.
6
7. 7
9
8. 14
1
9. 9
5
10. 11
Write the percent as a decimal.
11. 0.25%
426
Chapter 9
Percents
12. 250%
13. 0.0014%
14. 0.05%
Page 3 of 5
EXAMPLE
5
Using a Percent Less Than 1%
Water The total amount of water on Earth, including salt water and
fresh water, is about 326,000,000 cubic miles. Of this amount, 0.009% is
in fresh water lakes. What is the amount of water in fresh water lakes?
Solution
0.009% of 326,000,000 0.00009 326,000,000
29,340
Write percent as
a decimal.
Multiply.
ANSWER The amount of water in fresh water lakes is 29,340 cubic miles.
Your turn now
Solve the following problem.
15. Evan’s resting heart rate is 72 beats per minute. During intense
exercise, his heart rate is 250% of his resting heart rate. What is
Evan’s heart rate during intense exercise?
INTERNET
Exercises
eWorkbook Plus
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More Practice, p. 713
Getting Ready to Practice
1. Vocabulary Write a decimal that is greater than 100%. Write a decimal
that is less that 1%.
Write the percent as a decimal or the decimal as a percent.
2. 47%
3. 3%
4. 0.7%
5. 0.02%
6. 324%
7. 208%
8. 0.29
9. 0.642
10. 0.0083
11. 0.00105
12. 2.03
13. 15.5
Write the fraction as a percent. Round to the nearest tenth of
a percent.
1
14. 6
7
15. 9
5
16. 12
9
17. 16
18. Toy Cars The price of a miniature toy car in 1968 was 0.295% of its
current price. Today the car is a collector’s item and is priced at $200.
What was the price of the toy car in 1968?
Lesson 9.3
Percents and Decimals
427
Page 4 of 5
Practice and Problem Solving
with
Example
1
2
3
4
5
Homework
Exercises
19–26
27–34
35–42
19–26, 48
49
Write the percent as a decimal.
19. 11%
20. 8%
21. 210%
22. 0.3%
23. 0.15%
24. 42.5%
25. 3.01%
26. 125%
Write the decimal as a percent.
Online Resources
27. 0.26
28. 0.07
29. 0.049
30. 0.205
31. 0.005
32. 1.184
33. 2.14
34. 0.0085
CLASSZONE.COM
Write the fraction as a percent.
• More Examples
• eTutorial Plus
11
35. 15
13
36. 21
17
37. 18
23
38. 30
14
39. 39
5
40. 26
20
41. 49
74
42. 95
43. Mental Math What is 200% of 8? What is 300% of 8? What is 400% of 8?
Describe how you can find these answers without performing any
written calculations.
44. Number Sense The money you earned this summer is 120% of the
money you earned last summer. Did you earn more money or less
money this summer than you did last summer? Explain your reasoning.
Science
Explain In Exercises 45–47, tell whether the statement seems
reasonable. Explain why or why not.
45. “Work” was listed as an after school activity by 110% of your
classmates.
46. Of the 100 people surveyed, 0.05% said that they drive mopeds.
47. Your math test score is 125% of your last test score.
48. Hamsters The mass of a newborn black-bellied hamster is 0.934% of
the mass of an adult hamster. Write the percent as a decimal.
49. Population In 2001, Argentina’s population was about 0.61% of the
world population. The world population was about 6,137,000,000
people. Approximately how many people lived in Argentina in 2001?
■
Write the percent as a decimal and as a fraction or mixed number.
Hamsters
The mass of an adult
hamster is typically
between 112 grams and
908 grams. What is the
range of a hamster’s mass?
428
Chapter 9
Percents
50. 14%
51. 92.3%
52. 0.001%
53. 252%
Write the decimal as a fraction or mixed number and as a percent.
54. 0.8
55. 0.0877
56. 0.0021
57. 3.13
Page 5 of 5
58. Writing Describe a situation in real life where a percent less than 1% or
greater than 100% can be used.
Copy and complete the statement using <, >, or .
59. 0.14% _?_ 0.014
60. 3.4 _?_ 34%
61. 0.59 _?_ 59%
4
62. _?_ 49%
9
13
63. 84% _?_ 15
1
64. 0.99 _?_ 11
65. Consumer Spending In 1998, the average consumer spending per
person on books was about 460% as much as on video games. The
average consumer spending per person on video games was $18.45.
What was the average consumer spending per person on books?
66. Movie Sequels A movie made $1,582,000 at the box office. The sequel
to the movie made 104% of the original movie. How much money did
the sequel make?
Challenge Order the values from least to greatest.
1
67. 0.33%, 0.00311, , 0.0031
300
461
68. , 920%, 9.02, 9.202
50
Mixed Review
Use equivalent ratios to solve the proportion. (Lesson 8.4)
x
1
69. 20
5
x
5
70. 24
8
x
9
71. 36
12
x
98
72. 11
22
Use a proportion to find the percent of the number. (Lesson 9.2)
73. 70% of 280
74. 30% of 210
75. 21% of 400
76. 32% of 500
Basic Skills Estimate the product.
77. 5.43 20.9
78. 0.23 8.2
79. 7.32 49.9
80. 18.73 4.2
Test-Taking Practice
INTERNET
State Test Practice
CLASSZONE.COM
81. Multiple Choice Which list of values is in order from least to greatest?
A. 1018%, 10.2, 102, 1016
B. 10.2, 1018%, 102, 1016
C. 10.2, 102, 1018%, 1016
D. 10.2, 102, 1016, 1018%
82. Multiple Choice Pager sales represented 0.728% of the total sales of
electronics products in 1998. Which value is not equal to 0.728%?
F. 0.00728
728
1000
G. 728
100,000
H. Lesson 9.3
91
12,500
I. Percents and Decimals
429