Transcript 3-5 - Killeen ISD

3-5 Multiplying Decimals
Warm Up
Problem of the Day
Lesson Presentation
Course 1
3-5 Multiplying Decimals
Warm Up
Multiply.
1. 87  320
27,840
2. 943  800
754,400
3. 3,806  10
4. 1,207  100
38,060
120,700
5. 72  196
14,112
6. 120  523
62,760
Course 1
3-5 Multiplying Decimals
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
Course 1
3-5 Multiplying Decimals
Learn to multiply decimals by whole
numbers and by decimals.
Course 1
3-5 Multiplying Decimals
Additional Example 1: Science Application
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?
4  0.17
17
 4
68
Course 1
Multiply 4 by 0.17, since 1 pound on
Earth is 0.17 pound on the Moon.
Multiply as you would with whole
numbers.
3-5 Multiplying Decimals
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
 4
0.68
2 decimal places
+ 0 decimal places
2 decimal places
A 4 lb dumbbell on Earth weighs 0.68 lb on the Moon.
Course 1
3-5 Multiplying Decimals
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?
7  0.17
17
 7
119
Course 1
Multiply 7 by 0.17, since 1 pound on
Earth is 0.17 pound on the Moon.
Multiply as you would with whole
numbers.
3-5 Multiplying Decimals
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
 7
1.19
2 decimal places
+ 0 decimal places
2 decimal places
A 7 lb dumbbell on Earth weighs 1.19 lb on the Moon.
Course 1
3-5 Multiplying Decimals
Helpful Hint
You can use a decimal grid to model multiplication
of decimals.
Course 1
3-5 Multiplying Decimals
Additional Example 2A: Multiplying a Decimal by
a Decimal
Find the product.
0.3  0.4
Multiply. Then place the decimal point.
0.3
1 decimal place
 0.4
+ 1 decimal place
0.12
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2 decimal places
3-5 Multiplying Decimals
Additional Example 2B: Multiplying a Decimal by
a Decimal
0.07  0.8
0.07  1 = 0.07 Estimate the product. 0.8 is
close to 1.
0.07
 0.8
0.056
Multiply. Then place the
decimal point.
2 decimal places
+ 1 decimal place
3 decimal places; use a
placeholder zero
0.056 is close to the estimate of 0.07. The
answer is reasonable.
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3-5 Multiplying Decimals
Additional Example 2C: Multiplying a Decimal by
a Decimal
1.34  2.5
13=3
1.34
 2.5
670
2680
3.350
Estimate the product. Round
each factor to the nearest
whole number.
Multiply. Then place the
decimal point.
2 decimal places
+ 1 decimal place
3 decimal places
3.350 is close to the estimate of 3. The answer
is reasonable.
Course 1
3-5 Multiplying Decimals
Check It Out: Example 2A
Find the product.
0.5  0.2
Multiply. Then place the decimal point.
0.5
1 decimal place
 0.2
+ 1 decimal place
0.10
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2 decimal places
3-5 Multiplying Decimals
Check It Out: Example 2B
0.03  0.9
0.03  1 = 0.03 Estimate the product. 0.9 is
close to 1.
0.03
 0.9
0.027
Multiply. Then place the
decimal point.
2 decimal places
+ 1 decimal place
3 decimal places; use a
placeholder zero
0.027 is close to the estimate of 0.03. The
answer is reasonable.
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3-5 Multiplying Decimals
Check It Out: Example 2C
3.80  3.3
4  3 = 12
3.80
 3.3
1140
11400
12.540
Estimate the product. Round
each factor to the nearest
whole number.
Multiply. Then place the
decimal point.
2 decimal places
+ 1 decimal places
3 decimal places
12.54 is close to the estimate of 12. The answer
is reasonable.
Course 1
3-5 Multiplying Decimals
Additional Example 3A: Evaluating Decimal
Expressions
Evaluate 5x for the value of x.
x = 3.062
5x = 5(3.062)
Substitute 3.062 for x.
3.062
3 decimal places
5
+ 0 decimal places
15.310
3 decimal places

Remember!
These notations all mean multiply 3 times x.
3•x
Course 1
3x
3(x)
3-5 Multiplying Decimals
Additional Example 3B: Evaluating Decimal
Expressions
Evaluate 5x for the value of x.
x = 4.79
5x = 5(4.79)

Course 1
Substitute 4.79 for x.
4.79
2 decimal places
5
+ 0 decimal places
23.95
2 decimal places
3-5 Multiplying Decimals
Check It Out: Example 3A
Evaluate 5x for the value of x.
x = 2.012
5x = 5(2.012)
Substitute 2.012 for x.
2.012
3 decimal places
5
+ 0 decimal places
10.060
3 decimal places

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3-5 Multiplying Decimals
Check It Out: Example 3B
Evaluate 5x for the value of x.
x = 6.22
5x = 5(6.22)
6.22
2 decimal places
5
+ 0 decimal places
31.10
2 decimal places

Course 1
Substitute 6.22 for x.
3-5 Multiplying
Insert Lesson
Decimals
Title Here
Lesson Quiz
Find each product.
1.
0.8
 0.07
0.056
2. 0.006  0.07
0.00042
Evaluate 8x for each value of x.
3. x = 2.705
21.64
4. x = 0.804
6.432
5. “Pick your own” peaches sell for $0.95 per
pound. You picked 92 pounds of peaches. How
much were you charged?
$87.40
Course 1