## Calculator's cunning: the art of quick reckoning |

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### Contents

ADDITION 1623 | 16 |

Mental addition 21 Two general remarks about mental | 23 |

Subtraction by adding up 24 Audit 25 | 41 |

Copyright | |

10 other sections not shown

### Common terms and phrases

0-factor 100-complement 11-remainders 3-groups 9-packets append the square apply arithmetic auxiliary number boundary-division carry-over column complement-remainder cross-multiplication cross-sum decimal point distance divisibility rules division by 11 division-remainder easier errors of 9 errors of position estimate exactly example Exercises experienced calculator factor-division factorisation factors final remainder formula fraction ft ft given number gives halve Karl Menninger large multiplication table leaves remainder Martin Gardner means mental mental arithmetic method metic multiple of 9 neighbouring nine-test Note number of places number of zeros numbers ending odd number one-digit number order of magnitude original number original value p-ratio p-value partial answer partial remainder particular numbers percentage prime number proof reader remember RULE Add RULE Multiply RULE To multiply rules for divisibility semi-mentally simple squares of numbers stem-fractions stroke surprisingly simply teacher test for divisibility test holds three digits total remainder trick two-digit number U-product unit-boundary whole number write written