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N.S. 1.2
8/29/11
Adding and Subtracting Integers
Rule
Two like signs become a positive sign
+(+) 3+(+2) = 3 + 2 = 5
-(-)
6-(-3) = 6 + 3 = 9
Two unlike signs become a negative sign
+(-) 7+(-2) = 7 - 2 = 5
-(+) 8-(+2) = 8 - 2 = 6
Adding Integers
• 1) When adding integers of the same sign,
we add their values, and give the result the
same sign.
Examples:
• 2+5=7
• (-7) + (-2) = -(7 + 2) = -9
• (-80) + (-34) = -(80 + 34) = -114
2) When adding integers of the opposite signs, we turn
the numbers into positive, subtract the smaller from
the larger, and give the result the sign of the larger
number.
• Example: 8 + (-3) = ?
So, 8 and -3 become 8 and 3. Subtracting the
smaller from the larger gives
8 - 3 = 5, and since the larger number was +8, we
give the result the same sign as 8, so
8 + (-3) = 5.
Example:
-22 + 11 = ? -22 and 11 become 22 and 11.
Subtracting the smaller from the larger gives
22 - 11 = 11, and since the larger number is 22, we give the result the same sign as -22,
so -22 + 11 = -11.
Subtracting Integers
When subtracting integers, add
the opposite.
12 - (-5) = 12 + (5) = ____
-8 - 7 = -8 + (-7) = ____
-22 - (-40) = -22 + (40) = ____
Whiteboard CFU
38+(-5)=
Whiteboard CFU
(-1)-(-40)=
Whiteboard CFU
(-34)+50=
Whiteboard CFU
10+3-(-8)=
Whiteboard CFU
2- (-9)-8=
Independent Practice N.S. 1.2
Find each sum.
1. (-12) + 7
2 (-1) + (-7)
3. (-6)+12
4. -3+(-4)
 (-4)+6
6 (-4)+
7. (-1) + (-46)
 (-3)+1
Find each difference.
9. 2-(-2)=
1 (-1)-1
11 (-)-(-6)
12. 4-11=
13. 48-(-31)=
14. 16-21=
15. 1-41
16 (-3)-3
17 (-1)-(-3)
Evaluate each expression.
18. (-1) - 47
19. 13+(-2)
2 -32-44
21 (-2)-2
22 16+(-13)+
23 (-12)+(-11)