Page 50 - 振昆讲速算

一个数为625倍数的乘法（续）

1
1
11
A×6875=A× 110000 =A×10000× =A×10000× 16−4−1 =A×10000×(1- - )
16 16 16 4 16
1
13
1
A×8125=A× 130000 =A×10000× =A×10000× 16−4+1 =A×10000×(1- + )
16 16 16 4 16
15
1
A×9375=A× 150000 =A×10000× =A×10000× 16−1 =A×10000×(1 - )
16 16 16 16
17
1
A×10625=A× 170000 =A×10000× =A×10000× 16+1 =A×10000×(1+ )
16 16 16 16
1
1
例1. 7 3 5 2 5×8 1 2 5 =7 3 5 2 5 0 0 0 0×(1 - + ) =
4 16

7 3 5 2 5 0 0 0 0×1= 7 3 5 2 5 0 0 0 0
- 7 3 5 2 5 0 0 0 0 ÷4 = - 1 8 3 8 1 2 5 0 0

+ 1 6 2 1 8 7 5 0 0÷4 = + 4 5 9 5 3 1 2 5

5 9 7 3 9 0 6 2 5

例2. 4 7 3 5 6 7 9×9 3 7 5 =4 7 3 5 6 7 9×1 0 0 0 0×(1 - ) =
1
16
4 7 3 5 6 7 9 0 0 0 0×1 = 4 7 3 5 6 7 9 0 0 0 0

- 4 7 3 5 6 7 9 0 0 0 0× = - 2 9 5 9 7 9 9 3 7 5
1
16
4 4 3 9 6 9 9 0 6 2 5

46