Quick number crunchingdtcoulson@gmail.com
Fives                            42 x 5 To multiply by five,....
Fives                            42 x 5 = 21 To multiply by five,....  halve the number....
Fives                            42 x 5 = 210 To multiply by five,....  halve the number....  and multiply by ten.
Fives                            42 x 5 = 210                            86 x 5 To multiply by five,....  halve the number...
Fives                            42 x 5 = 210                            86 x 5 = 43 To multiply by five,....  halve the n...
Fives                            42 x 5 = 210                            86 x 5 = 430 To multiply by five,....  halve the ...
Fives                            42 x 5 = 210                            86 x 5 = 430 To multiply by five,....  halve the ...
Fives                            42 x 5 = 210                            86 x 5 = 430 To multiply by five,....  halve the ...
Fives        42 x 5 = 210        86 x 5 = 430        13 x 5 = 6 5
Fives                           42 ÷ 5  To divide by five,....
Fives                          42 ÷ 5 = 8 4 To divide by five,.... double the number,...
Fives                          42 ÷ 5 = 8.4 To divide by five,.... double the number,...  and divide by ten.
Fives                          42 ÷ 5 = 8.4                          86 ÷ 5 To divide by five,.... double the number,...  ...
Fives                          42 ÷ 5 = 8.4                          86 ÷ 5 = 17 2 To divide by five,.... double the numbe...
Fives                          42 ÷ 5 = 8.4                          86 ÷ 5 = 17.2 To divide by five,.... double the numbe...
Fives                          42 ÷ 5 = 8.4                          86 ÷ 5 = 17.2 To divide by five,.... double the numbe...
Fives                          42 ÷ 5 = 8.4                          86 ÷ 5 = 17.2 To divide by five,.... double the numbe...
Fives        42 ÷ 5 = 8.4        86 ÷ 5 = 17.2        13 ÷ 5 = 2 .6
Fifteens                42 x 15 To multiply by 15,....
Fifteens                42 x 15   420 To multiply by 15,....  multiply by ten,...
Fifteens                42 x 15   420                          210 To multiply by 15,....  multiply by ten,...    and halv...
Fifteens                42 x 15   420                          210 To multiply by 15,....   630  multiply by ten,...    an...
Fifteens                64 x 15 To multiply by 15,....  multiply by ten,...    and halve it,...      and add.
Fifteens                64 x 15   640 To multiply by 15,....  multiply by ten,...    and halve it,...      and add.
Fifteens                64 x 15   640                          320 To multiply by 15,....  multiply by ten,...    and halv...
Fifteens                64 x 15   640                          320 To multiply by 15,....   960  multiply by ten,...    an...
Fifteens                65 x 15 To multiply by 15,....  multiply by ten,...    and halve it,...      and add.
Fifteens                65 x 15   650 To multiply by 15,....  multiply by ten,...    and halve it,...      and add.
Fifteens                65 x 15   650                          325 To multiply by 15,....  multiply by ten,...    and halv...
Fifteens           65 x 15   650                     325                     975
Twenty-fives                32 x 25 To multiply by 25,....
Twenty-fives                32 x 25   3200 To multiply by 25,....  multiply by 100,...
Twenty-fives                32 x 25   3200 To multiply by 25,....    800  multiply by 100,...   and divide by 4.
Twenty-fives                124 x 25 To multiply by 25,....  multiply by 100,...   and divide by 4.
Twenty-fives                124 x 25   1 2400 To multiply by 25,....  multiply by 100,...   and divide by 4.
Twenty-fives               124 x 25   1 2400                           3 100
Twenty-fives                121 ÷ 25  To divide by 25,....
Twenty-fives                121 ÷ 25   484  To divide by 25,....   multiply by 4,...
Twenty-fives                121 ÷ 25   4 .8 4  To divide by 25,....   multiply by 4,...  and divide by 100.
Twenty-fives                33 ÷ 25  To divide by 25,....   multiply by 4,...  and divide by 100.
Twenty-fives                33 ÷ 25   1 32  To divide by 25,....   multiply by 4,...  and divide by 100.
Twenty-fives                33 ÷ 25   1.3 2  To divide by 25,....   multiply by 4,...  and divide by 100.
Elevens                   62 x 11 To multiply by 11,....
Elevens                   62 x 11                 62                62 To multiply by 11,....
Elevens                     62 x 11                  62                 62                682 To multiply by 11,....add th...
Elevens                     37 x 11 To multiply by 11,....add the number to itself,       diagonally.
Elevens                     37 x 11                  37                 37 To multiply by 11,....add the number to itself,...
Elevens                     37 x 11                  37                 37                407 To multiply by 11,....add th...
Elevens                     29625 x 11 To multiply by 11,....add the number to itself,       diagonally.
Elevens                     29625 x 11                 29625                29625 To multiply by 11,....add the number to ...
Elevens             29625 x 11           29625          29625          32587 5
Fours                    621 x 4 To multiply by 4,....
Fours                    621 x 4                           1242 To multiply by 4,.... double the number,...
Fours                    621 x 4                           1242                           2484 To multiply by 4,.... doubl...
Sixes                    312 x 6 To multiply by 6,....
Sixes                    312 x 6                         624 To multiply by 6,.... double the number,...
Sixes                    312 x 6                         624                         1872 To multiply by 6,.... double the...
Sixes                    125 x 6 To multiply by 6,.... double the number,...     and triple it.
Sixes                    125 x 6                           250 To multiply by 6,.... double the number,...     and triple ...
Sixes                    125 x 6                           250                           750 To multiply by 6,.... double ...
Refactoring              121 x 24                 With bigger numbers,...
Refactoring                  121 x 24              ( 11 x 11 x 24 )                      Tear the factors apart,...
Refactoring                  121 x 24              ( 11 x 11 x 24 )                 11 x 264                      Tear the...
Refactoring                  121 x 24              ( 11 x 11 x 24 )                 11 x 264      2 6 4    2 6 4          ...
Refactoring                  121 x 24              ( 11 x 11 x 24 )                 11 x 264      2 6 4    2 6 4          ...
Refactoring                        75 x 1 2  Look for factorsthat ‘click’ together       nicely.
Refactoring                               75 x 1 2                        ( 2 5 x 3 ) x (3 x 4 )  Look for factorsthat ‘cl...
Refactoring                               75 x 1 2                        ( 2 5 x 3 ) x (3 x 4 )                          ...
Refactoring                               75 x 1 2                        ( 2 5 x 3 ) x (3 x 4 )                          ...
Refactoring              24 x 12
Refactoring                   24 x 12              (2 x 12) x 12
Refactoring                   24 x 12              (2 x 12) x 12                 1 44 x 2
Refactoring                   24 x 12              (2 x 12) x 12                 1 44 x 2                   2 88
Refactoring              18 x 35
Refactoring              18 x 35               9 x 70
Refactoring              18 x 35               9 x 70               630
dtcoulson@gmail.com
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Transcript of "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

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