Question

速算！！！！！急！！！！ （要写过程）

1993×20002000－2000×19931993

79.31×0.6783×0.25＋23.56＋6.783×7.931×0.75－0.125×0.7931×67.83×8

987×19861986－1986×19871987

6.8×0.32＋0.32×4.2－8÷25

28.67×67＋3.2×286.7＋573.4×0.05

0.25×4.5×6.4×1250

Answer 1

1993×20002000－2000×19931993
=1993×2000×10001-2000×1993×10001＝0
（20002000=10001×2×1000=10001×2000）

79.31×0.6783×0.25＋23.56＋6.783×7.931×0.75－0.125×0.7931×67.83×8
=7.931×6.783×0.25＋23.56＋6.783×7.931×0.75－0.125×8×7.931×6.783
=7.931×6.783×(0.25+0.75-1)=0
（79.31×0.6783=79.31÷10×0.6783×10=7.931×6.783）

987×19861986－1986×19871987
=987×1986×10001-1986×1987×10001
=（987-1987）19861986
=-19861986000

6.8×0.32＋0.32×4.2－8÷25
=0.32×(6.8+4.2)-（8×4）÷（25×4）
=0.32×11-0.32×1
=0.32×10=3.2

28.67×67＋3.2×286.7＋573.4×0.05
=28.67×67＋32×28.67＋28.67×1
=28.67×(32+67+1)=28.67×100=2867（同第二道题，小数点的移动）

0.25×4.5×6.4×1250
=0.25×4.5×4×1.6×250×5
=0.25×4×1.6×5×250×4.5
=8×250×4.5=4×250×4.5×2
=1000×9=9000

Answer 2

1993×20002000－2000×19931993
=1993*2000*10001-2000*1993*10001
=0

79.31×0.6783×0.25＋23.56＋6.783×7.931×0.75－0.125×0.7931×67.83×8
=79.31*0.6783*0.25+23.56+0.6783*79.31*0.75-79.31*0.6783
=79.31*0.6783*（0.25+0.75-1）+23.56
=23.56

987×19861986－1986×19871987
=987*1986*10001-1986*1987*10001
=（987-1987）19861986
=-19861986000

6.8×0.32＋0.32×4.2－8÷25
=0.32*（6.8+4.2-1）
=3.2

28.67×67＋3.2×286.7＋573.4×0.05
=28.67*67+32*28.67+28.67
=28.67*（67+32+1）
=2867

0.25×4.5×6.4×1250
=（0.25*4）*（4.5*2）*（1250*0.8）
=1*9*1000
=9000

终于做完了，乘号就用星号代替了

Answer 3

1993*2000*10001-2000*1993*10001=0

Answer 4

250