multiplying and dividing decimals section 1-3 (pages 17-22)
TRANSCRIPT
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Multiplying and Dividing Decimals
Section 1-3 (Pages 17-22)
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Review…
Estimate each quotient using compatible numbers.
1. 24.8 ÷ 4.9
2. 103.8 ÷ 13.2
3. 128.62 ÷ 9.86
4. 41.77 ÷ 6.07
About 5
About 8
About 13
About 7
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Properties of Multiplication
Identity Property
The product of 1 and “a” is “a”.
5 x 1 = 5 1 x 5 = 5
Zero PropertyThe product of 0 and any number is 0.5 x 0 = 0 0 x 5 = 0
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Properties of Multiplication
Commutative Property
Changing the order of factors does not change the product.
5 x 2 = 2 x 5
Associative PropertyChanging the grouping of factors does not change the product.(3 x 2) x 5 = 3 x (2 x 5)
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To multiply decimals…
Step 1: Multiply as if the factors are whole numbers.
Step 2: Add the number of the decimal places in both factors to find the number of decimal places in the product.
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ExampleFind the product of 0.2 x 0.7
Step 2: Locate the decimal point. 0.2 x 0.7
0.14
Step 1: Multiply as with whole numbers. 2 x 7 14
1 decimal place
1 decimal place
2 decimal places
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ExampleFind the product of 1.45 x 2.6.
Step 2: Locate the decimal point.
Step 1: Multiply as with whole numbers.
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ExampleFind the product of 1.02 x 3.6.
Step 2: Locate the decimal point.
Step 1: Multiply as with whole numbers.
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Multiplying using the Properties…
Use mental math to find 2 x 4.097 x 0.5
We know that 2 x 0.5 will give us 1 and then the product of 1 and 4.097 is 4.097.
2 x 4.097 x 0.5 = 2 x 0.5 x 4.097
= (2 x 0.5) x 4.097
= 1 x 4.097
= 4.097
Commutative Property
Associative Property
Simplify
Identity Property
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ExampleUse mental math to find the product of 1.09 x 23.6 x 0.
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ExampleUse mental math to find the product of 2.5 x 6.3 x 4.
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Additional Problems
1. 1.45 x 2.6
2. 1.3 x 0.005
3. 41 x 7.5
4. 0 x 2.78 x 1
5. 5 x (4.3 x 1)