The method of calculating the quick addition of arbitrary numbers is very simple. As long as learners remember a general formula of fast addition-"standard addition (decimal number) minus complement, and the previous digit plus 1", they can completely solve the problem of fast addition of any digit from high to low. For example: (1), 67+48 = (6+5) ×10+(7-2) =15, (2) 758+496 = (7+5) ×

Fast calculation of subtraction

The fast subtraction of any number of digits is also a general formula for fast subtraction-"standard subtraction (for borrowed digits), addition and subtraction, and subtraction of the previous digit", which can completely solve the problem of fast subtraction of any number of digits from high to low. For example: (1), 67-48 = (6-5) ×/kloc-0+(7+2) =19, (2), 758-496 = (7-5 )×/kloc-0.

Multiplication fast calculation

The general formula of fast multiplication is ab× CD = (a+1)× c× 100+b× d+Webster's fast number ×10. Fast calculation number |=(a-c)×d+(b+d- 10)×c, and fast calculation number ‖=(a+b- 10)×c+(d-c)×a, and fast calculation number ⅲ = a. (1), the evolution number calculated by the first method =(a-c)×d+(b+d- 10)×c, which is suitable for any two-digit multiplication with the same beginning and end, such as: 26×28, 47×48, 87× 84- (2).

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