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Mental Math

Mental Math. Strand B – Number Sense Grade 2. 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. Plus 1 Facts. 2+1= 8+1= 6+1= 9+1= 4+1= 8+1= 5+1= 3+1= 1+1=

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Mental Math

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  1. Mental Math Strand B – Number Sense Grade 2

  2. 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

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

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

  5. 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

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

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

  8. 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

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

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

  11. 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

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

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

  14. 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

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

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

  17. 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.

  18. 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=

  19. 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=

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

  21. Make 10 Using a Ten Frame 7+3= 7+3=10

  22. Make 10 Using a Ten Frame 4+6= 4+6=10

  23. Make 10 Using a Ten frame 8+2= 8+2=10

  24. 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.

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

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

  27. 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).

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

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

  30. 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 ** **

  31. 10 and “Some More” 10 + 2 10 + 5 10 + 1 3 +10 10 + 6 8 + 10 10 + 5 10 + 9 7 + 10 10 + 4

  32. 10 and “Some More” 27 + 6 15 + 9 57 + 5 68 + 7 37 + 8 87 + 9 48 + 4 9 + 77 69 + 6 8 + 16

  33. 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

  34. 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

  35. 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

  36. 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

  37. 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

  38. 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

  39. 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

  40. 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

  41. 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

  42. Quick Addition – No RegroupingFront 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

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

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

  45. 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

  46. 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

  47. 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

  48. 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

  49. 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

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