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Sign Rules for Addition
If the terms have the same
sign
(both positive or both negative):
Add them & keep the sign
If the terms have
different signs
(one positive and one negative):
Subtract them (big minus small)
& keep the sign of the big number
Same Signs: Add & keep the sign
Combine
-4 and -5 = -9
1. Add the numbers: 2. keep the negative
4+5=9
Combine 6 and 8 = 14
Note: Numbers that have no sign in front (on their left)
are “understood” to be positive
1. Add the numbers: 2. keep the positive
6 + 8 = 14
Different Signs:
Subtract & keep the sign of the bigger number
Combine -3 and 7 = 4
2. keep the sign of
the bigger number
1. Subtract the numbers:
( +7 is bigger than -3)
7-3=4
(Big - small: 7 is bigger than 3)
Combine
-10 and 7
1. Subtract the numbers:
10 - 7 = 3
(Big - small: 10 is bigger than 7)
= -3
2. keep the sign of
the bigger number
( -10 is bigger than +7)
Sign Rules for Multiplication
Count the number of negative (minus) signs in the problem
If it has an odd
number of negatives:
The answer will be negative
If it has an even
number of negatives:
The answer will be positive
Odd number of negatives: Answers are negative
Combine -4(-5)(2)(-1) =
-40
2. Answer is negative
1. Count negatives:
-4(-5)(2)(-1)
(3 negatives): 3 is an ODD number
Combine -3(-4)(-7)
-14(-1)
=-6
2. Answer is negative
1. Count negatives:
-3(-4)(-7)
-14(-1)
(5 negatives): 5 is an ODD number
Even number of negatives: Answers are positive
Combine 4(-5)(-3)
= 60
2. Answer is positive
1. Count negatives:
4(-5)(-3)
(2 negatives): 2 is an EVEN number
Combine -5(2)(-6)
-4(-1)
= 15
2. Answer is positive
1. Count negatives:
-5(2)(-6)
-4(-1)
(4 negatives): 4 is an EVEN number
Practice Problems: (Hit enter to see the answers)
1) (-6)(7)
5) - 5(-1)(-2)
(-3)(4)
2) 5(-9)(-2)
6) -(-2)(8)
3) -(-3)(-10)
7) (4)(-1)(1)(-1)(-8)
4) -(-8)(-6)(-2)
(-2)
8) (-11)(-12)
Answers:
1) -42
2) 90
3) -30
4) -48
5) 5/6
6) 16
7) -32
8) 132
End of Tutorial
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