The document discusses two mental math strategies: compatible numbers and compensation. Compatible numbers are those that are easy to add mentally, like numbers near multiples of 10. Compensation involves adjusting one number up or down to make the calculation easier, such as adding 3 to one number and subtracting 3 from the other. Examples demonstrate using these strategies to mentally calculate additions and subtractions.

1. 2-2 Mental Math:
Using Compatible
#s and Compensation
Math Notes
Mathematical Reasoning 1.0

2. Compatible Numbers

3. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.

4. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.
19 + 25 + 11 =

5. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.
19 + 25 + 11 =

6. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.
19 + 25 + 11 = 30

7. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.
19 + 25 + 11 = 30 + 25

8. Compatible Numbers
Compatible numbers are numbers that
are easy to compute mentally.
19 + 25 + 11 = 30 + 25
= 55

9. Compensation Numbers

10. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.

11. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47

12. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 +

13. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16

14. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3

15. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust

16. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust

17. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust

18. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust
50

19. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust
50 +

20. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust
50 + 13 =

21. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
47 + 16
Add 3 Subtract 3
to adjust
50 + 13 = 63

22. Compensation Numbers

23. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.

24. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73

25. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 -

26. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38

27. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
to adjust

28. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust

29. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust

30. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust
75

31. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust
75 -

32. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust
75 -

33. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust
75 - 40 =

34. Compensation Numbers
Compensation involves deciding which number to
adjust to make it easier to add or subtract.
Compensate by changing the other number.
73 - 38
Add 2
Add 2
to adjust
75 - 40 = 35

35. Guided Practice
9 + 1 + 25 =

36. Guided Practice
9 + 1 + 25 =
Any numbers you
can easily add
FIRST to make this
easier?

37. Guided Practice
9 + 1 + 25 =
Any numbers you
9 + 1 = 10 can easily add
FIRST to make this
easier?

38. Guided Practice
9 + 1 + 25 =
Any numbers you
9 + 1 = 10 can easily add
FIRST to make this
easier?
10 + 25 = __

39. Guided Practice
9 + 1 + 25 =
Any numbers you
9 + 1 = 10 can easily add
FIRST to make this
easier?
35
10 + 25 = __

40. Guided Practice
7 + 13 + 19 =

41. Guided Practice
7 + 13 + 19 =
Any numbers you
can easily add
FIRST to make this
easier?

42. Guided Practice
7 + 13 + 19 =
Any numbers you
7 + 13 = 20 can easily add
FIRST to make this
easier?

43. Guided Practice
7 + 13 + 19 =
Any numbers you
7 + 13 = 20 can easily add
FIRST to make this
easier?
20 + 19 = __

44. Guided Practice
7 + 13 + 19 =
Any numbers you
7 + 13 = 20 can easily add
FIRST to make this
easier?
39
20 + 19 = __

45. Guided Practice
29 + 37 =

46. Guided Practice
Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.

47. Guided Practice
+1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.

48. Guided Practice
+1 -1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.

49. Guided Practice
+1 -1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.
30

50. Guided Practice
+1 -1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.
30 36

51. Guided Practice
+1 -1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.
30 36
30 + 36 = __

52. Guided Practice
+1 -1 Remember, this is
29 + 37 = COMPENSATION
with adding. ADD
something, TAKE
something away.
30 36
30 + 36 = 66
__

53. Guided Practice
67 + 14 =

54. Guided Practice
Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.

55. Guided Practice
+3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.

56. Guided Practice
+3 -3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.

57. Guided Practice
+3 -3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.
70

58. Guided Practice
+3 -3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.
70 11

59. Guided Practice
+3 -3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.
70 11
70 + 11 = __

60. Guided Practice
+3 -3 Remember, this is
67 + 14 = COMPENSATION
with adding. ADD
something, TAKE
something away.
70 11
81
70 + 11 = __

61. Guided Practice
38 - 19 =

62. Guided Practice
Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.

63. Guided Practice
+2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.

64. Guided Practice
+2 +2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.

65. Guided Practice
+2 +2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.
40

66. Guided Practice
+2 +2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.
40 21

67. Guided Practice
+2 +2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.
40 21
40 - 21 = __

68. Guided Practice
+2 +2 Remember, this is
38 - 19 = COMPENSATION
with subtracting.
ADD something to
BOTH numbers.
40 21
19
40 - 21 = __

69. Guided Practice
89 - 37 =

70. Guided Practice
Remember, this is
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.

71. Guided Practice
Remember, this is
-4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.

72. Guided Practice
Remember, this is
-4 -4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.

73. Guided Practice
Remember, this is
-4 -4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.
85

74. Guided Practice
Remember, this is
-4 -4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.
85 33

75. Guided Practice
Remember, this is
-4 -4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.
85 33
85 - 33 = __

76. Guided Practice
Remember, this is
-4 -4
COMPENSATION
89 - 37 = with subtracting.
ADD (or SUBTRACT)
something to BOTH
numbers.
85 33
85 - 33 = 52
__