2. 5.4 Multiplying Signed Decimal Numbers
Chapter 5 Rational Numbers: Positive and
Negative Decimals

3. 5.4 Multiplying Signed Decimal Numbers
Objectives
Multiply positive and negative decimals.
Estimate the answer when multiplying decimals.
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4. Objective 1: Multiply positive and negative decimals.
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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5. Objective 1: Multiply positive and negative decimals.
Example
Find the product of 8.34 and (–4.2).
Step 1
Multiply the numbers as if they were whole numbers.
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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6. Objective 1: Multiply positive and negative decimals.
Example
(continued)
Step 2
Count the total number of decimal places in both factors.
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7. Objective 1: Multiply positive and negative decimals.
(continued)
Example
Step 3 Count over 3 places in the product and write the decimal point. Count from right to left.
Step 4 The factors have different signs, the product is negative: 8.34 × (–4.2) = –
Copyright © 2010 Pearson Education, Inc. All rights reserved.
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8. Objective 1: Multiply positive and negative decimals.
Example
Find the product (–0.042)(–0.03).
Multiply and count the decimal places.
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9. Objective 1: Multiply positive and negative decimals.
(continued)
Example
The answer has only three decimal places, but five are needed. Write two zeros on the left side of the answer.
(–0.042)(–0.03) =
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10. Objective 2: Estimate the answer when multiplying decimals.
Example
Estimate the product (76.34)(12.5) using front end rounding. Then find the exact answer.
Copyright © 2010 Pearson Education, Inc. All rights reserved.
Sec