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Key
Idea
You can use basic
facts, patterns,
and properties to
multiply mentally. |
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Multiplication
Patterns |
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Vocabulary
• factor
• product
• Commutative
Property of
Multiplication
• Associative
Property of
Multiplication |
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What’s the
pattern? |
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a. Use
a calculator to find each product. |
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3
x 5
30 x 5
300 x 5
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3 x 50
30 x 50
300 x 50 |
3 x 500
30 x 500
300 x 500 |
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b.
Find the following products without
a calculator.
Then check your answers with a calculator. |
| 5
x 8, 50 x 8, 50 x 80, 500 x 8, 500 x 80, 500 x 800 |
| c.
Describe a rule that tells how to
find each product. |
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How can properties
help you multiply more easily? |
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| Commutative Property of Multiplication |
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Associative Property of
Multiplication |
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You can change the order of
the factors. |
| 34 x
8 = 8 x 34 |
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You can change the grouping
of
factors. |
| (7 x
25) x 4 = 7 x (25 x 4) |
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| Find 20 x 5 x 6. |
Using the Associative
Property,
you can think: |
(20
x 5) x 6 = 100 x 6 = 600 OR
20 x (5 x 6) = 20 x 30 = 600. |
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| Find 2 x
70 x 50. |
Use
the properties to change the
order and the groupings. |
| 2
x 70 x 50 |
= 2 x (70
x 50)
= 2 x (50 x 70)
= (2 x 50) x 70
= 100 x 70
= 7,000 |
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Talk
About It |
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1.
How is the Associative Property used
in Example B?
2.
How is the Commutative Property used
in Example B?
3.
Can you use the Associative Property
for 2 x (5 + 6)? Explain. |
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