4 1 multiplying rational numbers examples
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multiply rational numbers.
SOL: none
ObjectiveThe student will be able to:
Designed by Skip Tyler, Varina High School and Nicole Kessinger Deep Run High School
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Multiplying Rules
1) If the numbers have the same signs then the product is positive.
(-7) • (-4) = 28
2) If the numbers have different signs then the product is negative.
(-7) • 4 = -28
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Examples
1) (3x)(-8y)
20 4
5
2) Write both numbers as a fraction.
Cross-cancel if possible.
20
1
4
5
80
5= -16
Multiplying fractions:
top # • top #
Bottom # • bottom#
-24xy
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2
5
5
8
3)
10
40=
1
4=
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Multiply: (-3)(4)(-2)(-3)
1. 72
2. -72
3. 36
4. -36
Answer NowAnswer Now
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an easy way to determine the sign of the answer
3 negative signs -> Odd -> answer is negative-480
When you have an odd number of negatives, the answer is negative.
When you have an even number of negatives, the answer is positive.
4) (-2)(-8)(3)(-10)Do you have an even or odd number of
negative signs?
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Last one!
5) 1
2
6 5 2
5
2
Positive or negative answer?Positive - even # of negative signs (4)
Write all numbers as fractions and multiply.
=12
1
2
6
1
5
1
2
5
2
1
12010
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What is the sign of the product of (-3)(-4)(-5)(0)(-1)(-6)(-91)?
1. Positive
2. Negative
3. Zero
4. Huh?
Answer NowAnswer Now