Warm Up

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Warm Up
Problem of the Day
Lesson Presentation
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Warm Up Multiply.
1. 87 ? 320
27,840
2. 943 ? 800
754,400
3. 3,806 ? 10
38,060
120,700
4. 1,207 ? 100
5. 72 ? 196
14,112
6. 120 ? 523
62,760
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Problem of the Day Carmen and Rita sold homemade
oatmeal cookies. After 8 days, they had sales
totaling 70. Each day, their sales were 0.50
higher than the previous day. What were their
sales on the first day?
7.00
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Learn to multiply decimals by whole numbers and
by decimals.
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Additional Example 1 Science Application Somethin
g that weighs 1 lb on Earth weighs 0.17 lb on the
Moon. How much would a 4 lb dumbbell weigh on the
Moon?
Multiply 4 by 0.17, since 1 pound on Earth is
0.17 pound on the Moon.
4 ? 0.17
17
Multiply as you would with whole numbers.
? 4
68
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Additional Example 1 Continued Something that
weighs 1 lb on Earth weighs 0.17 lb on the Moon.
How much would a 4 lb dumbbell weigh on the Moon?
Place the decimal point by adding the number of
decimal places in the numbers multiplied.
0.17
2 decimal places
? 4
0 decimal places
0.68
2 decimal places
A 4 lb dumbbell on Earth weighs 0.68 lb on the
Moon.
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Check It Out Example 1 Something that weighs 1
lb on Earth weighs 0.17 lb on the Moon. How much
would a 7 lb dumbbell weigh on the Moon?
Multiply 7 by 0.17, since 1 pound on Earth is
0.17 pound on the Moon.
7 ? 0.17
17
Multiply as you would with whole numbers.
? 7
119
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Check It Out Example 1 Continued Something that
weighs 1 lb on Earth weighs 0.17 lb on the Moon.
How much would a 7 lb dumbbell weigh on the Moon?
Place the decimal point by adding the number of
decimal places in the numbers multiplied.
0.17
2 decimal places
? 7
0 decimal places
1.19
2 decimal places
A 7 lb dumbbell on Earth weighs 1.19 lb on the
Moon.
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Additional Example 2A Multiplying a Decimal by a
Decimal Find the product. 0.3 ? 0.4
0.3
0.4
?
0.12
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Additional Example 2B Multiplying a Decimal by a
Decimal 0.07 ? 0.8
0.07 ? 1 0.07
0.07
? 0.8
0.056
0.056 is close to the estimate of 0.07. The
answer is reasonable.
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Additional Example 2C Multiplying a Decimal by a
Decimal 1.34 ? 2.5
1 ? 3 3
1.34
?
2.5
670
2680
3.350
3.350 is close to the estimate of 3. The answer
is reasonable.
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Check It Out Example 2A Find the product. 0.5 ?
0.2
0.5
?
0.2
0.10
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Check It Out Example 2B 0.03 ? 0.9
0.03 ? 1 0.03
0.03
0.9
?
0.027
0.027 is close to the estimate of 0.03. The
answer is reasonable.
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Check It Out Example 2C 3.80 ? 3.3
4 ? 3 12
3.80
?
3.3
1140
11400
12.540
12.54 is close to the estimate of 12. The answer
is reasonable.
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Additional Example 3A Evaluating Decimal
Expressions Evaluate 5x for the value of x. x
3.062
5x 5(3.062)
3.062
?
5
15.310
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Additional Example 3B Evaluating Decimal
Expressions Evaluate 5x for the value of x. x
4.79
5x 5(4.79)
4.79
?
5
23.95
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Check It Out Example 3A Evaluate 5x for the
value of x. x 2.012
5x 5(2.012)
2.012
?
5
10.060
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Check It Out Example 3B Evaluate 5x for the
value of x. x 6.22
5x 5(6.22)
6.22
?
5
31.10
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Insert Lesson Title Here
Lesson Quiz
Find each product. 1. 0.8 2. 0.006 ?
0.07 Evaluate 8x for each value of x.
? 0.07
0.056
0.00042
3. x 2.705 4. x 0.804
6.432
21.64
5. Pick your own peaches sell for 0.95 per
pound. You picked 92 pounds of peaches. How much
were you charged?
87.40