1. Home
  2. Flashcards
  3. Preview

mentalmath.txt

  1. 10%
    Divide by 10
  2. 5%
    Divide by 10, then divide by 2
  3. 15%
    Divide by 10, then add 1/2
  4. 20%
    Divide by 10, then double
  5. Multiplying large numbers (ex. 12 x 640)
    10x600 + 10x40 + 2x600 + 2x40
  6. Multiplying by 5
    Divide number by 2, then multiply by 10
  7. Percentage as per 100 (ex. 7% of 300, 8% of 250)
    • 7% of 300 = 7 + 7 + 7 = 21
    • 8% of 250 = 8 + 8 + 4 
  8. Percentages can be flipped (ex. 10% of 50)
    10% of 50 = 50% of 10 = 5
  9. Addition from left to right of large numbers (ex. 45 + 34, 459 + 637)
    • 45 + 34 = (45 + 30) --> (75 + 4) = 79
    • 459 + 637 = (459 + 600) --> (1059 + 30) --> (1089 + 7) = 1096 
Author
blswes
ID
163001
Card Set
mentalmath.txt
Description
mental math
Updated

  1. n Home
  2. Flashcards
  3. Preview