1. Mental Math Strand B – Number Sense Grade 2

3. Addition – Plus 1 Facts 7+1 or 1+7 is asking for the number after 7. One more than 7 is 8. 7+1=8, 1+7=8 4 +1 is asking for the number after 4. One more than 4 is 5. 4+1=5

4. Plus 1 Facts 2+1= 8+1= 6+1= 9+1= 4+1= 8+1= 5+1= 3+1= 1+1= 7+1=

5. Plus 1 Facts 8+1= 1+4= 1+9= 6+1= 1+8= 2+1= 7+1= 1+5= 1+1= 3+1=

6. Addition – Plus 2 Facts 6+2 is skip counting by 2 after 6 or asking for the next even number after 6 to get 8. 6+2=8 1+2 is skip counting by 2 after 1. 1+2=3

7. Plus 2 Facts 1+2= 3+2= 7+2= 2+2= 5+2= 9+2= 4+2= 0+2= 8+2= 6+2=

8. Plus 2 Facts 1+2= 3+2= 2+7= 2+2= 2+5= 9+2= 2+6= 2+4= 0+2= 2+8=

9. Addition-Doubles Facts 1+1: The number of wheels on two unicycles 2+2: The number of wheels on two bicycles 3+3: The number of wheels on two tricycles 4+4: The number of wheels on two cars 5+5: The number of fingers on two hands 6+6: The number of eggs in an egg carton 7+7 The number of days in two weeks 8+8 the number of crayons in a two-row box 9+9: the number of tires on an 18-wheeler

10. Double Facts 4+4= 1+1= 5+5= 0+0= 6+6= 7+7= 9+9= 8+8= 3+3= 2+2=

11. Double Facts 2+2= 9+9= 0+0= 5+5= 7+7= 3+3= 4+4= 1+1= 6+6= 8+8=

12. Addition- Near Doubles This strategy is also called the “doubles plus one” facts. Double the smaller number and add one more. 6+7 is (6+6)+1 6+5 is double 5 and add 1 or 10+1=11

13. Near Doubles 8+9= 8+7= 2+3= 3+4= 2+1= 5+6= 4+5= 6+5= 0+1= 6+7=

14. Near Doubles 5+4= 2+1= 3+4= 2+3= 7+8= 8+9= 5+6= 4+3= 7+6= 0+1=

15. Addition- Doubles Plus 2  This strategy is also called 2-apart facts  3+5: Double the smaller number plus 2 3+5 = 6 (double 3) +2 =8  4+6= 8 (double 4) +2 =10

16. Doubles Plus 2 4+6= 5+7= 6+8= 7+5= 3+5= 7+9= 5+3= 6+4= 9+7= 0+2=

17. Doubles Plus 2 1+2= 5+3= 6+4= 5+7= 8+6= 7+9= 3+5= 2+0= 2+1= 9+7=

18. Addition – Plus or Minus 0 “No Change” Adding does not always make numbers bigger. 5+0=5. Adding zero involved no change. Subtracting does not always make numbers smaller. 4-0=4. Subtracting zero involved no change.

19. Plus or Minus 0. “No Change” 5+0= 2+0= 0+6= 4+0= 0+9= 10+0= 6-0= 1-0= 8-0= 7-0=

20. Plus or Minus 0 “No Change” 3-0= 8-0= 10+0= 0+6= 4-0= 1-0= 0+9= 2+0= 7-0= 6+0=

21. Addition – Making 10 Using Ten Frames Visualize 6 counters on this ten frame. This leaves 4 boxes on the ten-frame empty for a total of 6+4=10 ***** *

22. Make 10 Using a Ten Frame 7+3= 7+3=10 ***** **

23. Make 10 Using a Ten Frame 4+6= 4+6=10 ****

24. Make 10 Using a Ten frame 8+2= 8+2=10 ***** ***

25. Addition –Make 10 9+3: Think, 9+1 (from the 3) is 10, and 10 +2 (the other part of the 3) is 12 or 9+3= (9+1)+2=10+2=12 7+4: Think 7 and 3 (from the 4) is 10, and 10+1 (the other part of the 4) is 11 or 7+4= (7+3) +1=10+1=11 *Students may wish to use a ten frame to solve.

26. Make 10 9+4= 5+9= 8+5= 9+6= 6+8= 3+9= 8+4= 8+6= 7+9= 8+3=

27. Make 10 7+5= 8+7= 7+6= 3+7= 7+7= 9+7= 7+4= 5+7= 6+7= 7+8=

28. Addition – Counting On 2+6: Start with the larger number and COUNT ON the amounts of the smaller number (six, SEVEN, EIGHT). 2+45: Start with 45 and COUNT ON forty- five, FORTY-SIX, FORTY-SEVEN).

29. Counting On 7+3= 3+6= 8+2= 1+5= 1+9= 3+9= 1+8= 5+2= 7+1= 5+3=

30. Counting On 1+6= 4+2= 2+7= 3+8= 2+6= 43+3= 2+51= 2+47= 26+3= 3+45=

31. Addition – 10 and “Some More” 10 + 4, think 10 and 4 is 14 10 + 8, think 10 and 8 is 18 28 + 4, think 28 + 2 is 30 and 30 + 2 is 32 ***** ***** ***** ***** ***** ***** **

32. 10 and “Some More” 10 + 2 10 + 5 10 + 1 3 +10 10 + 6 8 + 10 10 + 5 10 + 9 7 + 10 10 + 4

33. 10 and “Some More” 27 + 6 15 + 9 57 + 5 68 + 7 37 + 8 87 + 9 48 + 4 9 + 77 69 + 6 8 + 16

34. Addition – Using Addition Facts for 10’s (Doubles) If you know that 6 + 6 = 12, then you know that 60 + 60 =120 If you know that 5 + 5 = 10, then you know that 50 + 50 = 100 If you know that 4 + 4 = 8, then you know that 40 + 40 = 80

35. Using Addition Facts for 10’s (Doubles) 40 + 40 50 + 50 80 + 80 20 + 20 70 + 70 10 + 10 30 + 30 90 + 90 60 + 60

36. Using Addition Facts for 10’s (Doubles) 90 + 90 70 + 70 30 + 30 10 + 10 80 + 80 50 + 50 20 + 20 40 + 40 60 + 60

37. Using Addition Facts for 10’s (Near Doubles) If you know that 2 + 3 = 5, then you know that 20 + 30 is (20 + 20) + 10 = 50. Say “ 20 + 30 is double 20 and add 10; 40 + 10 is 50.” 30 + 40 is (30 + 30) + 10 = 70

38. Using Addition Facts for 10’s (Near Doubles) 30 + 40 10 + 20 50 + 40 70 + 80 60 + 70 80 + 90 50 + 60 20 + 30 40 + 50 90 + 80

39. Using Addition Facts for 10’s (Near Doubles) 80 + 90 50 + 40 90 + 80 70 + 60 40 + 50 20 + 10 40 + 30 30 + 20 60 + 50 70 + 80

40. Using Addition Facts for 10’s (Doubles plus 2) If you know that 3 + 5 = 8, then you know that 30 + 50 is (30 + 30) + 20 = 80 40 + 60 is (40 + 40) + 20 = 100

41. Using Addition Facts for 10’s ( Doubles Plus 2) 40 + 60 70 + 90 50 + 30 60 + 40 50 + 70 90 + 70 60 + 80 70 +50 20 + 40 10 + 30

42. Using Addition Facts for 10’s ( Doubles Plus 2) 50 + 70 80 + 60 70 + 90 70 + 50 40 + 60 30 + 50 90 + 70 60 + 40 30 + 10 20 + 40

43. Quick Addition – No Regrouping Front End Addition 56 + 23, add the highest place values first 5 + 2 = 7, then add add the sum of the next place value, 6 + 3= 9. 56 + 23 = 79 71 + 12 = 7 + 1 =8, 1 +2 = 3 = 83

44. Front End Addition 71 + 12 37 + 51 63 + 33 15 + 62 44 + 53 66 + 23 56 + 22 82 + 11 27 + 12 73 + 24

45. Front End Addition 62 + 35 44 + 23 92 + 17 32 + 56 81 + 19 28 + 70 56 + 32 22 + 74 14 + 63 51 + 37

46. Front End Addition with Regrouping To solve 46 + 38 you can join the tens (7 tens) and the ones (14 ones), and rename the sum. 46 + 38 = 70 + 14 =84

47. Front End Addition with Regrouping 74 + 8 15 + 16 74 + 19 53 + 9 45 + 7 63 + 7 27 + 8 34 + 6 72 + 19 14 + 27

48. Front End Addition with Regrouping 75 + 7 16 + 15 76 + 18 54 + 9 44 + 8 46 + 38 19 + 14 21 + 9 63 + 28 34 + 7

49. Addition _ Finding Compatibles This strategy involves looking for pairs if numbers that add to powers of 10 (10 or 100) 3 + 8 + 7, think 3 + 7 is 10 plus 8 is 10 + 8 = 18 6 + 9 + 4, think 6 + 4 is 10 plus 9 is 10 + 9 =19

50. Finding Compatibles 6 + 9 + 4 3 + 8 + 7 2 + 3 + 8 4 + 6 + 2 1 + 9 + 5 5 + 6 + 5 2 + 8 + 7 6 + 5 + 4 6 + 7 + 3 4 + 9 + 1

51. Finding Compatibles 5 + 6 + 5 1 + 9 + 5 4 + 6 + 2 8 + 3 + 2 4 + 9 + 6 6 + 7 + 4 9 + 1 + 3 7 + 5 + 3 8 + 4 + 2 5 + 5 + 1

52. Addition - Compensation This strategy involves changing one number to a ten; carrying out the addition and adjusting the answer to compensate for the original change. This strategy is useful when one of the numbers ends in 8 or 9. 7 + 9, think 7 + 10 is 17, but I added one too many, so I subtract one from 17 to get 16 or 7 + 9 = (7 + 10) –1 =16

53. Compensation 2 + 9 3 + 9 9 + 4 5 + 8 9 + 5 8 + 7 9 + 6 8 + 3 7 + 8 7 + 9

54. Compensation 8 + 7 8 + 3 6 + 9 8 + 7 5 + 9 8 + 5 4 + 9 9 + 3 9 + 2 9 + 7

55. Subtraction- Doubles This strategy uses the addition double facts to help find the answers to related subtraction combinations. 12 – 6, think 6 plus what makes 12? 6 + 6 =12, so 12 – 6 = 6 If you know 8 – 4 = 4, then 80 – 40 = 40

56. Subtraction – Doubles 10 – 5 16 – 8 6 – 3 8 – 4 14 – 7 18 – 9 12 – 6 4 – 2 20 – 10 2 - 1

57. Subtraction – Doubles 20 – 10 40 – 20 160 – 80 140 – 70 20 – 10 120 – 60 100 – 50 180 – 90 60 – 30 80 – 40

58. Subtraction – Near Doubles This strategy also uses the addition double facts to help find the answer. 9 – 4, think: 4 + 4 = 8, 4 + 5 = 9, so 9 – 4 = 5 If you know that 9 – 4 = 5, then for 90 – 40, think 40 + 40 = 80; 40 + 50 = 90, so 90 – 40 = 50

59. Subtraction – Near Doubles 13 – 6 17 – 8 11 – 5 7 – 3 15 – 7 17 – 8 19 – 9 9 – 4 21 – 10 5 – 2

60. Subtraction – Near Doubles 70 – 30 110 – 50 50 – 20 150 – 70 130 – 60 170 – 80 90 – 40 190 – 90 30 – 10 70 - 30

61. Subtraction – “Think Addition” Use your knowledge of addition facts to find the answers to subtraction equations. 9 – 4, think: 4 + what = 9? 80 – 20, think: 20 + what = 80?

62. Subtraction – Think Addition 10 – 4 =___( 4 plus what equals 10?) 10 – 4 8 – 5 9 – 3 8 – 2 10 – 3 6 – 4 10 – 6 7 – 3 8 – 4

63. Subtraction – Think Addition 80 – 20 90 – 30 100 – 30 60 – 40 80 – 50 70 – 40 100 – 40 60 – 30 90 – 50 70 - 20

64. Using Subtraction Facts for 10s If we know that 8 - 3 = 5, then for 80 – 30, think: 8 tens subtract 3 tens is 5 tens or 50 90 – 10, think: 9 tens subtract 1 ten is 8 tens or 80.

65. Using Subtraction Facts for 10s 90 – 10 30 – 20 60 – 30 20 – 10 70 – 60 80 – 30 50 – 20 40 – 30 20 – 10 80 - 50

66. Using Subtraction Facts for 10s 80 – 20 70 – 50 20 – 10 60 – 40 30 – 10 90 – 70 50- 20 80 – 30 60 – 30 90 - 40

67. Addition & Subtraction Front End Estimation This strategy involves combining only the values in the highest place value to get a “ball-park figure” 43 + 54, think 40 + 50 is 90 92 – 53, think: 90 - 50 is 40

68. Addition Front End Estimation 62 + 31 54 + 33 13 + 82 44 + 23 71 + 14 34 + 42 73 + 12 21 + 43 12 + 51 22 + 46

69. Subtraction Front End Estimation 92 – 53 93 – 62 72 – 33 43 – 12 64 – 23 54 – 21 32 – 23 81 – 54 91 – 42 84 - 61

70. Addition & Subtraction Rounding This strategy involves rounding each number to the highest, or highest two place values and adding the rounded numbers. To estimate 27 + 31, think: 27 rounds to 30 and 31 rounds to 30, so 30 + 30 is 60. To estimate 87 – 32, think: 87 rounds to 90 and 32 rounds to 30, so 90 – 30 is 60.

71. Addition -Rounding 48 + 23 61 + 48 97 + 12 28 + 57 34 + 59 18 + 22 14 + 32 41 + 34 27 + 31 45 + 63

72. Subtraction - Rounding 57 –14 36 – 22 68 – 34 84 – 9 43 – 8 99 – 47 82 – 59 54 – 18 93 –12 87 – 32