作业帮数学题（不来会后悔的!）1990*198.9-1989*198.8=?对了有分奖哦!
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数学题（不来会后悔的!）1990*198.9-1989*198.8=?对了有分奖哦!
数学题（不来会后悔的!）
1990*198.9-1989*198.8=?对了有分奖哦!
数学题（不来会后悔的!）1990*198.9-1989*198.8=?对了有分奖哦!
(1989+1)198.9-1989*198.8
=1989*198.9+198.9-1989*198.8
=1989(198.9-198.8)+198.8
=198.9+198.8
=397.7
简便方法
原式=(1990-1989)*198.8+1990*(198.9-198.8)
=198.8+1990*0.1=198.8+199
=397.8
395811-395413.2=397.8
1990*198.9-198.9*1988=2*198.9=397.8
1990*198.9-1989*198.8
=（1989+1）*198.9-1989*198.8
=1989*198.9-1989*198.8+198.9
=1989*（198.9-198.8）+198.9
=1989*0.1+198.9
=198.9+198.9
=397.8
1990*198.9-1989*198.8
=1990*198.9-(1990-1)*(198.9-0.1)
=199+198.9-0.1
=397.8
1990*198.9-1989*198.8=199*10*198.9-1989*198.8=199*1989-1989*198.8=1989*(199-198.8)=199*0.2=(200-1)*0.2=200*0.2-0.2=39.8