mentalmath.txt

10%

Divide by 10
5%

Divide by 10, then divide by 2
15%

Divide by 10, then add 1/2
20%

Divide by 10, then double
Multiplying large numbers (ex. 12 x 640)

10x600 + 10x40 + 2x600 + 2x40
Multiplying by 5

Divide number by 2, then multiply by 10
Percentage as per 100 (ex. 7% of 300, 8% of 250)
- 7% of 300 = 7 + 7 + 7 = 21
- 8% of 250 = 8 + 8 + 4
Percentages can be flipped (ex. 10% of 50)

10% of 50 = 50% of 10 = 5
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

163001

Card Set

mentalmath.txt

Description

mental math

Updated

2012-07-18T21:03:34Z

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