Warm Up

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Warm Up
Problem of the Day
Lesson Presentation
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Warm Up Order the decimals from least to greatest
. 1. 18.74, 18.7, 18.47 2. 9.06, 9.66, 9.6
, 9.076 Write each in words. 3. 3.072 4. 6.
1258
18.47, 18.7, 18.74
9.06, 9.076, 9.6, 9.66
three and seventy-two thousandths
six and one thousand two hundred fifty-eight
ten-thousandths
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Problem of the Day Calculate your age in months
.
Possible answer 11 yr 8 mo 140 mo
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Learn to estimate decimal sums, differences,
products, and quotients.
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Insert Lesson Title Here
Vocabulary
clustering front-end estimation
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When numbers are about the same value, you can
use clustering to estimate. Clustering means
rounding the numbers to the same value.
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Additional Example 1 Health Application
Nancy wants to cycle, ice skate, and water ski
for 30 minutes each. About how many calories will
she burn in all? (Cycling 165.5 calories, ice
skating 177.5 calories, and water skiing
171.5 calories)
165.5
170
177.5
170
171.5
170
510
Nancy burns about 510 calories
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Try This Example 1 Abner wants to run, roller bl
ade, and snow ski for 60 minutes each. About how
many calories will he burn in all? (Running
185.5 calories, roller blading 189.5 calories,
and snow skiing 191.5 calories)
185.5
190
189.5
190
191.5
190
570
Abner burns about 570 calories
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Additional Example 2 Rounding Decimals to
Estimate Sums and Differences Estimate by roundin
g to the indicated place value.
A. 7.13 4.68 ones B. 9.705 0.2683 tenth
s
7.13 4.68
7 5 12
9.705 9.7
9.4
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Try This Example 2 Estimate by rounding to the i
ndicated place value. A. 6.09 3.72 ones B
. 8.898 0.4619 tenths
6.09 3.72
6 4 10
8.898 8.9
8.4
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Additional Example 3 Using Compatible Numbers to
Estimate Products and Quotients
Estimate each product or quotient.
A. 33.83 ? 1.98 B. 72.77 26.14
35 ? 2 70
So 33.83 ? 1.98 is about 70.
75 25 3
So, 72.77 26.14 is about 3.
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Try This Example 3 Estimate each product or quot
ient.
A. 22.12 ? 4.98 B. 62.31 18.52
20 ? 5 100
So 22.12 ? 4.98 is about 100.
60 20 3
So, 62.31 18.52 is about 3.
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You can also use front-end estimation to estimate
with decimals. Front-end estimation means to use
only the whole-number part of the decimal.
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Additional Example 4 Using Front-End Estimation
Estimate a range for the sum.
7.86 36.97 5.40 Use front-end estim
ation.
7.86
7
36.97
36
5.40
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at least 48
The exact answer of 7.86 36.97 5.40 is 48 or
greater.
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Additional Example 4 Continued
You can estimate a range for the sum by adjusting
the decimal part of the numbers. Round the
decimals to 0, 0.5, or 1.
0.86
1.00
0.97
1.00
0.50
0.40
2.50
48.00 2.50 50.50
The estimated range for the sum is from 48.00 to
50.50.
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Try This Example 4 Estimate a range for the sum.

8.92 47.88 3.41 Use front-end estimation.
8.92
8
47.88
47
3.41
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at least 58
The exact answer of 8.92 47.88 3.41 is 58 or
greater.
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Try This Example 4 You can estimate a range for
the sum by adjusting the decimal part of the
numbers. Round the decimals to 0, 0.5, or 1.
0.92
1.00
0.88
1.00
0.41
0.50
2.50
58.00 2.50 60.50
The estimated range for the sum is from 58.00 to
60.50.
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Insert Lesson Title Here
Lesson Quiz Part 1
Estimate by rounding to the indicated place value.
1. 3.07442 1.352 tenths 2. 7.305 4.12689
nearest whole number
4.5
3
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Insert Lesson Title Here
Lesson Quiz Part 2
Estimate each product or quotient.
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3. 6.75 ? 1.82
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4. 10.5 3.42
5. The snowfall in December, January, and
February was 18.26 cm, 29.36 cm, and 32.87 cm,
respectively. About how many total centimeters
of snow fell during the three months?
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