secrets-of-mental-math-malestrom

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250 Answers Decimalization (page 98) 1. 2 5 .40 2. 4 7 .571428 3. 3 8 .375 4. 9 .75 12 5 6 5. .4166 6. .5454 7. 1 4 .5833 8. 1 3 .481 1 2 1 1 24 27 9. 1 8 .375 10. 1 0 6 .714285 11. .1875 12. 1 9 .422 48 14 3 2 45 Testing for Divisibility (page 101) Divisibility by 2 1. 53,428 2. 293 3. 7241 4. Yes No No Divisibility by 4 5. 3932 6. 67,348 7. 358 8. Yes Yes No Divisibility by 8 9. 59,366 10. 73,488 11. 248 12. No Yes Yes Divisibility by 3 13. 83,671 14. No: 8 3 6 7 1 25 9846 Yes 57,929 No 6111 No 94,737 Yes: 9 4 7 3 7 30 15. 7359 16. Yes: 7 3 5 9 24 3,267,486 Yes: 3 2 6 7 4 8 6 36 Divisibility by 6 17. 5334 18. Yes: 5 3 3 4 15 19. 248 20. No: 2 4 8 14 67,386 Yes: 6 7 3 8 6 30 5991 No: odd Divisibility by 9 21. 1234 22. 8469 No: 1 2 3 4 10 Yes: 8 4 6 9 27
Answers 251 23. 4,425,575 No: 4 4 2 5 5 7 5 32 24. 314,159,265 Yes: 3 1 4 1 5 9 2 6 5 36 Divisibility by 5 25. 47,830 26. 43,762 27. 56,785 28. Yes No Yes 37,210 Yes Divisibility by 11 29. 53,867 30. Yes: 5 3 8 6 7 11 4969 No: 4 9 6 9 8 31. 3828 32. Yes: 3 8 2 8 11 Divisibility by 7 33. 5784 34. No: 5784 7 5777 577 7 570 57 941,369 Yes: 9 4 1 3 6 9 0 7336 Yes: 7336 14 7350 735 35 700 7 35. 875 36. Yes: 875 35 840 84 14 70 7 Divisibility by 17 37. 694 38. No: 694 34 660 66 1183 Yes: 1183 7 1190 119 21 140 14 629 Yes: 629 51 680 68 39. 8273 40. 13,855 No: 8273 17 8290 Yes: 13,855 85 13,940 829 51 880 1394 34 1360 88 136 34 170 17
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This book has been optimized for vi
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SECRE+S OF MEN+AL MA+H The Mathemag
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I dedicate this book to my wife, De
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Contents Foreword by Bill Nye (the
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Foreword by Bill Nye (the Science G
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Foreword xiii Well, actually, I hop
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Foreword xv there are also an infin
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xviii Foreword math nut. Immunizati
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xx Prologue in on his secrets of
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xxii Prologue where he learned thes
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xxiv Introduction Too often, math i
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2 Secrets of Mental Math 35 2 What
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4 Secrets of Mental Math Absolutely
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6 Secrets of Mental Math Similarly,
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8 Secrets of Mental Math Although I
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10 Secrets of Mental Math Exception
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12 Secrets of Mental Math math in y
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14 Secrets of Mental Math 67 28 8
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16 Secrets of Mental Math 858 7 re
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18 Secrets of Mental Math lot easie
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20 Secrets of Mental Math Carl Frie
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22 Secrets of Mental Math Of course
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24 Secrets of Mental Math 958 417
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26 Secrets of Mental Math to 10. We
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28 Secrets of Mental Math By roundi
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30 Secrets of Mental Math mentally,
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32 Secrets of Mental Math 48 40 8
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34 Secrets of Mental Math problems
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36 Secrets of Mental Math 3-BY-1 MU
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38 Secrets of Mental Math sometimes
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40 Secrets of Mental Math 376 (300
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44 Secrets of Mental Math BE THERE
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46 Secrets of Mental Math 41 2 1 42
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48 Secrets of Mental Math other squ
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50 Secrets of Mental Math WHY THESE
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52 Secrets of Mental Math Similarly
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54 Secrets of Mental Math Gardner o
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56 Secrets of Mental Math same digi
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New and Improved Products: Intermed
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60 Secrets of Mental Math 59 (60 1
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62 Secrets of Mental Math 88 (90 2
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64 Secrets of Mental Math To see ho
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66 Secrets of Mental Math Remember
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68 Secrets of Mental Math 67: 67 3
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70 Secrets of Mental Math EXERCISE:
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72 Secrets of Mental Math Rounding
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74 Secrets of Mental Math 2. The ea
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76 Secrets of Mental Math 13 1,000
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78 Secrets of Mental Math Chapter 8
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Chapter 4 Divide and Conquer: Menta
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82 Secrets of Mental Math Let’s t
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86 Secrets of Mental Math In using
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88 Secrets of Mental Math 682 23 I
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92 Secrets of Mental Math original
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94 Secrets of Mental Math way is to
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96 Secrets of Mental Math 6 7 8 .
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98 Secrets of Mental Math You can e
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100 Secrets of Mental Math A number
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102 Secrets of Mental Math Divisibi
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104 Secrets of Mental Math It is al
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106 Secrets of Mental Math So, To a
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Chapter 5 Good Enough: The Art of
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110 Secrets of Mental Math Notice t
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112 Secrets of Mental Math 8,367 5
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114 Secrets of Mental Math onds doe
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116 Secrets of Mental Math We obser
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118 Secrets of Mental Math Divide:
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120 Secrets of Mental Math roots. I
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122 Secrets of Mental Math MORE TIP
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124 Secrets of Mental Math I will s
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126 Secrets of Mental Math number o
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128 Secrets of Mental Math and sinc
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130 Secrets of Mental Math EXERCISE
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132 Secrets of Mental Math COLUMNS
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134 Secrets of Mental Math As illus
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136 Secrets of Mental Math 4. 3 5 8
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138 Secrets of Mental Math Next, we
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140 Secrets of Mental Math You have
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144 Secrets of Mental Math Step 4.
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146 Secrets of Mental Math Shakunta
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148 Secrets of Mental Math Here’s
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150 Secrets of Mental Math EXERCISE
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152 Secrets of Mental Math work by
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154 Secrets of Mental Math words: m
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156 Secrets of Mental Math 93: bum,
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158 Secrets of Mental Math And: 69
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162 Secrets of Mental Math 362 beco
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164 Secrets of Mental Math learned
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166 Secrets of Mental Math Once you
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168 Secrets of Mental Math Thomas F
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170 Secrets of Mental Math numbers
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172 Secrets of Mental Math Then do
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178 Secrets of Mental Math Using th
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180 Secrets of Mental Math Adding 8
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182 Secrets of Mental Math If both
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184 Secrets of Mental Math I diagra
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186 Secrets of Mental Math In our n
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188 Secrets of Mental Math produces
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190 Secrets of Mental Math be conve
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192 Secrets of Mental Math (e.g., 4
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194 Secrets of Mental Math As with
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196 Secrets of Mental Math I should
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198 Secrets of Mental Math Since yo
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Page 246 and 247: 220 Secrets of Mental Math For date
Page 248 and 249: Chapter ∞ Epilogue: How Math Help
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Page 256 and 257: 230 Secrets of Mental Math 7. Is th
Page 259 and 260: Answers CHAPTER 1: A LITTLE GIVE AN
Page 261 and 262: Answers 235 Three-Digit Subtraction
Page 263 and 264: 13. 757 14. 259 15. 297 297 16. or
Page 265 and 266: Answers 239 2 100 5. 98 2 9600 2 2
Page 267 and 268: Answers 241 2-by-2 Addition-Method
Page 269 and 270: 2-by-2 Factoring-Method Multiplicat
Page 271 and 272: Answers 245 13. 38 63 (9 7) 15.
Page 273 and 274: Answers 247 234 17 3. 217 2 46,800
Page 275: Answers 249 CHAPTER 4: DIVIDE AND C
Page 279 and 280: Answers 253 7. 7 8 1 1 4 1
Page 281 and 282: Answers 255 9. 104,972 10. 5,462,74
Page 283 and 284: Square Root Guesstimation (page 150
Page 285 and 286: 3-by-2 Exercises Using Factoring, A
Page 287 and 288: 21. 281 or 281 (280 1) 44 (11 4
Page 289 and 290: Answers 263 3. 58,324 2 “Liver”
Page 291 and 292: 3-by-3 Multiplication (page 192) 1.
Page 293 and 294: Answers 267 13. 783 (87 9) 589 1
Page 295 and 296: Answers 269 5-by-5 Multiplication (
Page 297 and 298: Bibliography RAPID CALCULATION Cutl
Page 299 and 300: Index addition: an “amazing” su
Page 301 and 302: Index 275 factoring a number: in th
Page 303 and 304: Index 277 three-by-two problems, 16
Page 305: About the Authors DR. ARTHUR BENJAM
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