(1999×99+2000×100+2000-1900)÷4000 计算结果

括号里=(2000-1)x99+2000x100+100
=2000x99-99+2000x100+100
=2000x(99+100)-99+100
=2000x(200-1)+1
=2000x200-2000+1
=4000x100-4000x1/2+1
除以4000=100-1/2+1/4000
=100-2000/4000+1/4000
=100-1999/4000
=99^2001/4000

=(1999*(100-1)+2000*100+2000-1900)/4000
=((1999+2000)100-1999+2000-1900)/4000
=(399900+1-1900)/4000
=(398000+1)/4000
=398/4+1/4000
=(400-2)/4=+1/4000
=100-1/2+1/4000
=99.50025