Chapter 3
Decimals
McGrawHill/Irwin
©2011 The McGrawHill Companies, All Rights Reserved
#3 Decimals
Learning Unit Objectives
Rounding Decimals; Fraction and
LU3.1
Decimal Conversions
1. Explain the place values of whole
numbers and decimals; round decimals
2. Convert decimal fractions to decimals,
proper fractions to decimals, mixed
numbers to decimals, and pure and
mixed decimals to decimal fractions
32
#3 Decimals
Learning Unit Objectives
Adding, Subtracting, Multiplying, and
LU3.2
Dividing Decimals
1. Add, subtract, multiply, and divide
decimals
2. Multiply and divide decimals by shortcut
methods
3. Complete decimal applications in foreign
currency
33
Table 3.1 Bag of M&M’s
Decimal
Color
Yellow
Fraction (hundredth)
18
.33
55
Red
10
.18
55
Blue
9
.16
Blue
55
Orange 7
.13
55
Brown 6
.11
55
Green
5
.09
55
Total
55
1.00
55 = 1
34
Percent
(hundredth)
32.73%
18.18%
16.36%
12.73%
10.91%
9.09%
100.00%
Decimal placevalue chart
Figure
3.1
35
Tenths
and
1
10
Hundred Thousandths
Decimal Point
1
Ten Thousandths
Ones
10
Thousandths
Tens
Hundreds
Thousands
1,000 100
Hundredths
Decimal Place Values
Whole Number Groups
1 . 1 . 1 . 1 .
100,000
1,000
10,000
100
Rounding Decimals
Step 1. Identify the place
value of the digit you want
to round
.3272727
Step 3. Drop all digits to the right
of the identified digit
.337272
Step 2. Identify the digit to the right.
If 5 or more, increase the identified digit
by 1. If less than 5 do not change
36
.33
Rounding Decimals
37
Round to nearest dollar:
$166.39
$166
Round to nearest cent:
$1,196.885
$1,196.89
Round to nearest hundredth: $38.563
$38.56
Round to nearest thousandth: $1,432.9981
$1,432.998
Converting Decimal Fractions to Decimals
2 Steps
38
Fraction Decimal # of places
1. Count the number of zeros 3
in the denominator.
10
.3
1
2. Place the numerator of the
decimal fraction to the
right of the decimal point
the same number of
places as you have zeros
in the denominator. Do
not go over the total
number of denominator
zeros.
3
100
.03
2
3
1,000
.003
3
3
10,000
.0003
4
Converting Proper Fractions to Decimals
3
4
S
L
A
U
EQ
1
p
Ste
.75
39
.75
4 3.00
2.8
20
20
0
Converting Mixed Numbers to Decimals
2
85
(
)
1
p
e
t
S
8.4
310
.4
5 2.0
2.0
0
8 + .4 (Step 2)
Converting Pure Decimals to Decimal Fractions
Step 1
Step 2
24
1
Places
2
.24
Step 3
311
24
24
100
Converting Mixed Decimals to
Decimal Fractions
Step 1
17.45
Step 2
45
1
Places
2
Step 3
312
45
45 45
=17
100 100
Adding Decimals
Add: 4 + 7.3 + 36.139 + .0007 + 8.22
4.0000
7.3000
36.1390
.0007
8.2200
55.6597
313
Subtracting Decimals
Subtract: 45.3 15.273
45.300
15.273
30.027
314
Multiplying Decimals
8.52 (2 decimal places)
x 6.7 (1 decimal places)
57084
3776
3 decimal places
5 decimal places
57.084
.03776
Need to add zero
2.36
x .016
315
Dividing Decimals
Step 1. Make the divisor a
whole number by moving
the decimal point to the right
Step 2. Move the decimal point
in the dividend to the right
the same number of places
as in step 1. If there are not
enough places, add zeros to the right
of the dividend.
Step 3. Place the decimal point
in the quotient above the
new decimal point in the
dividend. Divide as usual.
316
Example
2.5 32.800
25. 328.00
13.12
25. 328.00
25
78
75
30
25
50
50
Decimals Applications in Foreign Currency
The Wall Street Journal clip shows in China the price of Microsoft
Office was reduced to 199 yuan from an original price of 699
yuan. Using the currencies table lets us see what the original as
well as sales price is in U.S. dollars. In the table on page 74 1 yuan
equals $.1463. To find the original selling price you multiply the
number of yuan (699) times $.1463.
699 yuan x $.1463 = $102.26
The original selling price in U.S. Dollars is $102.26. To find the
new selling price in U.S. dollars, you multiply the number of yuan
199 times $.1463. The new selling price in U.S. dollars is $29.11.
$199 x $.1463 = $29.11
Table factor from currency table on page 74
Check $29.11 x 6.8348 = 198.96 yuan
Each 1 equal 6.8348 yuan
317
Shortcuts for Multiples of 10
Multiplication
•Count the zeros in the multiplier
•Move the decimal point the same
number of spaces to the right
6890
6.89 x 1000
6.89 x 10
6.89 x 100
318
689
68.9
Shortcuts for Multiples of 10
Division
•Count the zeros in the divisor
•Move the decimal point the same
number of spaces to the left
.00689
6.89 / 1000
6.89 / 10
6.89 / 100
319
.0689
.689