Download 3-3 Comparing and Ordering Decimals

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STUDY GUIDE 2010
Comparing & Ordering Decimals; Adding & Subtracting Decimals; Multiplying
decimals; Dividing Decimals; Word Problems
 COMPARING & ORDERING DECIMALS
How to Order a Set of Decimals:
1.
Line up the decimal points, and annex 0’s (so each decimal has the
same amount of places).
2a.
Compare, using one digit at a time, from left to right.
OR
2b.
Compare the whole numbers, then compare the decimals.
Example 1
Which is greater, 2.037 or 2.0335?
*2.0370
2.0335
Example 2 Which is greater, 30.48 or 3.4596?
*30.4800
3.4596
Example Comparing Multiple Numbers:
Tennessee
Ohio State
Penn State
Oklahoma
Texas
.697
.7142
.6886
.7150
.716
1) Line up the decimal points, adding zeros where needed.
.6970
.7142
.6886
.7150
.7160
2. Compare, starting at the left, then rewrite in order from least to greatest:
.6886, .6970, .7142, .7150, .7160
 ADDING AND SUBTRACTING DECIMALS
Adding and subtracting decimals is like adding and subtracting whole
numbers, but….
1. Line up the decimal points (this lines up the place values!)
2. Annex zeros, when necessary, as place holders.
3. When you finish adding or subtracting, bring down the decimal
point into the answer.
Example 1:
3.7 – 2.95
3.70
- 2.95
0.75
Example 2:
$ 41.39 + $ 23.17
$41.39
+ $23.17
$64.56
 MULTIPLYING DECIMALS
Introduction: Multiplying Numbers Containing Decimals
1. Multiply just as you would with whole numbers. (You do not
need to line up the decimals!!!)
2. Count the number of decimal places in both factors (numbers
that you multiply).
3. Place the decimal point so that:
# of decimal places in the product = # of decimal places in
the factors
How many decimal places would be in the following products?
1.
67.9 x 5
____1____ decimal place
2.
55.2 x 10.1
____2____ decimal places
3.
1.452 x 9
____3____ decimal places
Example 1:
78.42 x 9
78.42
x
9
705.78
Example 2:
1.45 x 0.7
1.45
x 0.7
1.015
There are 3 decimal
places in the factors,
so there must be 3
decimal places in the
product
 DIVIDING DECIMALS by WHOLE NUMBERS
Part 1: Dividing Decimals by Whole Numbers
1. Place the decimal point in the quotient directly above the
decimal point in the dividend. (Bring it straight up!)
2. Divide as you would with whole numbers. Remember…

Divide

Multiply

Subtract

Check

Bring down
Example 1:
14.8 ÷ 2
Example 2:
2 14.8
152.83 ÷ 17
17 152.83
Part 2: Dividing Decimals and Whole Numbers by Decimals
1. Move the decimal point to the far right of the divisor.
2. Move the decimal point in the dividend the same number of
places as in the divisor.
3. Place the decimal point in the quotient directly above the
decimal point in the dividend. (Bring it straight up!)
4. Divide as you would with whole numbers.
5. Add zeros as place holders, if necessary.
6. Round the quotient to the hundredths place, if necessary.
Example 1:
3.80 ÷ 0.19
0.19 3.80
Example 2:
0.30 $2.97
$2.97 ÷ 0.30