求简便运算?45.4+99.9*999+54.51-2+3-4+5-6+......+1991-1992+1993（这道

45.4+99.9*999+54.5
=45.4+54.5+99.9*999
=99.9*1+99.9*999
=99.9*(1+999)
=99.9*1000
=99900
1-2+3-4+5-6+.+1991-1992+1993
=(1-2)+(3-4)+(5-6)+.+(1991-1992)+1993
=-1-1-1-.-1+1993
那么有几个负一呢,在第一个括号内被减数是2,在第2个括号内被减数是4,在第3个括号内被减数是6,最后一个被减数是1992,所以有1992/2=996个负一,-996+1993=7
45.3*3.2+578*0.68+12*9.25
=45.3*3.2+57.8*6.8+12*9.25
=45.3*3.2+（45.3+12.5）*6.8+12*9.25
=45.3*3.2+45.3*6.8+12.5*6.8+12*9.25
=45.3*（3.2+6.8）+12.5*4*1.7+4*3*0.25*37
=453+85+111
=649

把99.9分成45.4和54.5就可以了，运算结果为：99900

1-2+3-4+5-6.....+1991-1992+1993
=(1-2)+(3-4)+(5-6).....+(1991-1992)+1993
=(-1)*(1992/2)+1993=997