作业帮简算(必须)1992×198.9-1991×198.8=?
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简算(必须)1992×198.9-1991×198.8=?
简算(必须)
1992×198.9-1991×198.8=?
简算(必须)1992×198.9-1991×198.8=?
1992×198.9-1991×198.8
=（1991+1）×198.9-1991×（198.9-0.1）
=1991×198.9+198.9-1991×198.9+199.1
=398
1992×198.9-1991×198.8
=(1991+1)×(198.8+0.1)-1991×198.8
=1991×198.8+1991×0.1+1×198.8+0.1-1991×198.8
=1991×0.1+1×198.8+0.1
=199.1+198.9
=398
1992×198.9-1991×198.8
=（1991+1）×198.9-1991×（198.9-0.1）
=1991×198.9+198.9-1991×198.9+199.1
=398