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# Quick number crunching (pdf)

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### Quick number crunching (pdf)

1. 1. Quick number crunchingdtcoulson@gmail.com
2. 2. Fives 42 x 5 To multiply by five,....
3. 3. Fives 42 x 5 = 21 To multiply by five,.... halve the number....
4. 4. Fives 42 x 5 = 210 To multiply by five,.... halve the number.... and multiply by ten.
5. 5. Fives 42 x 5 = 210 86 x 5 To multiply by five,.... halve the number.... and multiply by ten.
6. 6. Fives 42 x 5 = 210 86 x 5 = 43 To multiply by five,.... halve the number.... and multiply by ten.
7. 7. Fives 42 x 5 = 210 86 x 5 = 430 To multiply by five,.... halve the number.... and multiply by ten.
8. 8. Fives 42 x 5 = 210 86 x 5 = 430 To multiply by five,.... halve the number.... and multiply by ten. 13 x 5
9. 9. Fives 42 x 5 = 210 86 x 5 = 430 To multiply by five,.... halve the number.... and multiply by ten. 13 x 5 = 6.5
10. 10. Fives 42 x 5 = 210 86 x 5 = 430 13 x 5 = 6 5
11. 11. Fives 42 ÷ 5 To divide by five,....
12. 12. Fives 42 ÷ 5 = 8 4 To divide by five,.... double the number,...
13. 13. Fives 42 ÷ 5 = 8.4 To divide by five,.... double the number,... and divide by ten.
14. 14. Fives 42 ÷ 5 = 8.4 86 ÷ 5 To divide by five,.... double the number,... and divide by ten.
15. 15. Fives 42 ÷ 5 = 8.4 86 ÷ 5 = 17 2 To divide by five,.... double the number,... and divide by ten.
16. 16. Fives 42 ÷ 5 = 8.4 86 ÷ 5 = 17.2 To divide by five,.... double the number,... and divide by ten.
17. 17. Fives 42 ÷ 5 = 8.4 86 ÷ 5 = 17.2 To divide by five,.... double the number,... and divide by ten. 13 ÷ 5
18. 18. Fives 42 ÷ 5 = 8.4 86 ÷ 5 = 17.2 To divide by five,.... double the number,... and divide by ten. 13 ÷ 5 = 2 6
19. 19. Fives 42 ÷ 5 = 8.4 86 ÷ 5 = 17.2 13 ÷ 5 = 2 .6
20. 20. Fifteens 42 x 15 To multiply by 15,....
21. 21. Fifteens 42 x 15 420 To multiply by 15,.... multiply by ten,...
22. 22. Fifteens 42 x 15 420 210 To multiply by 15,.... multiply by ten,... and halve it,...
23. 23. Fifteens 42 x 15 420 210 To multiply by 15,.... 630 multiply by ten,... and halve it,... and add.
24. 24. Fifteens 64 x 15 To multiply by 15,.... multiply by ten,... and halve it,... and add.
25. 25. Fifteens 64 x 15 640 To multiply by 15,.... multiply by ten,... and halve it,... and add.
26. 26. Fifteens 64 x 15 640 320 To multiply by 15,.... multiply by ten,... and halve it,... and add.
27. 27. Fifteens 64 x 15 640 320 To multiply by 15,.... 960 multiply by ten,... and halve it,... and add.
28. 28. Fifteens 65 x 15 To multiply by 15,.... multiply by ten,... and halve it,... and add.
29. 29. Fifteens 65 x 15 650 To multiply by 15,.... multiply by ten,... and halve it,... and add.
30. 30. Fifteens 65 x 15 650 325 To multiply by 15,.... multiply by ten,... and halve it,... and add.
31. 31. Fifteens 65 x 15 650 325 975
32. 32. Twenty-fives 32 x 25 To multiply by 25,....
33. 33. Twenty-fives 32 x 25 3200 To multiply by 25,.... multiply by 100,...
34. 34. Twenty-fives 32 x 25 3200 To multiply by 25,.... 800 multiply by 100,... and divide by 4.
35. 35. Twenty-fives 124 x 25 To multiply by 25,.... multiply by 100,... and divide by 4.
36. 36. Twenty-fives 124 x 25 1 2400 To multiply by 25,.... multiply by 100,... and divide by 4.
37. 37. Twenty-fives 124 x 25 1 2400 3 100
38. 38. Twenty-fives 121 ÷ 25 To divide by 25,....
39. 39. Twenty-fives 121 ÷ 25 484 To divide by 25,.... multiply by 4,...
40. 40. Twenty-fives 121 ÷ 25 4 .8 4 To divide by 25,.... multiply by 4,... and divide by 100.
41. 41. Twenty-fives 33 ÷ 25 To divide by 25,.... multiply by 4,... and divide by 100.
42. 42. Twenty-fives 33 ÷ 25 1 32 To divide by 25,.... multiply by 4,... and divide by 100.
43. 43. Twenty-fives 33 ÷ 25 1.3 2 To divide by 25,.... multiply by 4,... and divide by 100.
44. 44. Elevens 62 x 11 To multiply by 11,....
45. 45. Elevens 62 x 11 62 62 To multiply by 11,....
46. 46. Elevens 62 x 11 62 62 682 To multiply by 11,....add the number to itself, diagonally.
47. 47. Elevens 37 x 11 To multiply by 11,....add the number to itself, diagonally.
48. 48. Elevens 37 x 11 37 37 To multiply by 11,....add the number to itself, diagonally.
49. 49. Elevens 37 x 11 37 37 407 To multiply by 11,....add the number to itself, diagonally.
50. 50. Elevens 29625 x 11 To multiply by 11,....add the number to itself, diagonally.
51. 51. Elevens 29625 x 11 29625 29625 To multiply by 11,....add the number to itself, diagonally.
52. 52. Elevens 29625 x 11 29625 29625 32587 5
53. 53. Fours 621 x 4 To multiply by 4,....
54. 54. Fours 621 x 4 1242 To multiply by 4,.... double the number,...
55. 55. Fours 621 x 4 1242 2484 To multiply by 4,.... double the number,... and double it again.
56. 56. Sixes 312 x 6 To multiply by 6,....
57. 57. Sixes 312 x 6 624 To multiply by 6,.... double the number,...
58. 58. Sixes 312 x 6 624 1872 To multiply by 6,.... double the number,... and triple it.
59. 59. Sixes 125 x 6 To multiply by 6,.... double the number,... and triple it.
60. 60. Sixes 125 x 6 250 To multiply by 6,.... double the number,... and triple it.
61. 61. Sixes 125 x 6 250 750 To multiply by 6,.... double the number,... and triple it.
62. 62. Refactoring 121 x 24 With bigger numbers,...
63. 63. Refactoring 121 x 24 ( 11 x 11 x 24 ) Tear the factors apart,...
64. 64. Refactoring 121 x 24 ( 11 x 11 x 24 ) 11 x 264 Tear the factors apart,...
65. 65. Refactoring 121 x 24 ( 11 x 11 x 24 ) 11 x 264 2 6 4 2 6 4 Tear the factors apart,... and use the tricks you’ve seen.
66. 66. Refactoring 121 x 24 ( 11 x 11 x 24 ) 11 x 264 2 6 4 2 6 4 Tear the factors apart,... 29 0 4 and use the tricks you’ve seen.
67. 67. Refactoring 75 x 1 2 Look for factorsthat ‘click’ together nicely.
68. 68. Refactoring 75 x 1 2 ( 2 5 x 3 ) x (3 x 4 ) Look for factorsthat ‘click’ together nicely.
69. 69. Refactoring 75 x 1 2 ( 2 5 x 3 ) x (3 x 4 ) 100 x 9 Look for factorsthat ‘click’ together nicely.
70. 70. Refactoring 75 x 1 2 ( 2 5 x 3 ) x (3 x 4 ) 100 x 9 900 Look for factorsthat ‘click’ together nicely.
71. 71. Refactoring 24 x 12
72. 72. Refactoring 24 x 12 (2 x 12) x 12
73. 73. Refactoring 24 x 12 (2 x 12) x 12 1 44 x 2
74. 74. Refactoring 24 x 12 (2 x 12) x 12 1 44 x 2 2 88
75. 75. Refactoring 18 x 35
76. 76. Refactoring 18 x 35 9 x 70
77. 77. Refactoring 18 x 35 9 x 70 630
78. 78. dtcoulson@gmail.com