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Un petit peu de calcul mental …

Un petit peu de calcul mental …. 75×12. 75 × 10 + 75 × 2 = 750 + 150 = 900. 70 × 12 + 5 × 12 = 840 + 60 = 900. 75 × 4 × 3 = 300 × 3 = 900. 25 × 124. 25 × 4 × 31 = 100 × 31 = 3100. 25 × 124 =. = 3100. 5 × 5 × 124 = 5 × 620 = 3100. 0,125 × 3,2. 125 x 32 = 125 × 8 x 4 = 1000 x 4 = 4000

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Un petit peu de calcul mental …

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  1. Un petit peu de calcul mental … 75×12 75 × 10 + 75 × 2 = 750 + 150 = 900 70 × 12 + 5 × 12 = 840 + 60 = 900 75 × 4 × 3 = 300 × 3 = 900

  2. 25 × 124 25 × 4 × 31 = 100 × 31 = 3100 25 × 124 = = 3100 5 × 5 × 124 = 5 × 620 = 3100

  3. 0,125 × 3,2 125 x 32 = 125 × 8 x 4 = 1000 x 4 = 4000 donc 0,125 × 3,2 = 0,4

  4. Je pense à un nombre. Je multiplie ce nombre par 6. J’ajoute 2 au résultat. Je multiplie le résultat précédent par 3. Je trouve 132. A quel nombre ai-je pensé ? × 6 42 + 2 44 × 3 132 7 : 3 - 2 : 6

  5. Cascade additive : 217 a+b b a 99 118 ? 64 35 54 25 10 39 15 Remarque : on peut trouver un générateur de pyramides additives et multiplicatives avec corrigés à cette adresse : http://manu.ledaine.free.fr/Pyramides/

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