速算与巧算![26×（6－2.5）÷0.5－25]×0.2 1993×20002000－2000×1993199379.

[26×（6－2.5）÷0.5－25]×0.2
=[26*7-25]/5
=[(25+1)*7-25]/5
=[25*6+7]/5
=30+7/5
=31.4
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+0.75)-79.31*0.6783*(1/8*8)
=0
1987×19861986－1986×19871987
=1987*1986*10001-1986*1987*10001
=0
6.8×0.32＋0.32×4.2－8÷25
=0.32*(6.8+4.2)-8/25
=0.32*11-8/25
=(32/100)*11-32/100
=32/100*(11-1)
=32/10
=3.2
28.67×67＋3.2×286.7＋573.4×0.05
=286.7*(6.7+3.2+2*0.05)
=2867
0.25×4.5×6.4×1250
=0.25 *4.5*(4*2*8)*125
=(0.25*4 )* (4.5*2) * (8*125)
=1*9*1000
=9000