1990×1989.9-1989×198.8简便运算
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1990×1989.9-1989×198.8简便运算
1990×1989.9-1989×198.8简便运算
1990×1989.9-1989×198.8简便运算
1990×1989.9-1989×198.8
=1990×(1989+0.9)-1989×198.8
=1990×1989+1990×0.9-1989×198.8
=(1990-198.8)×1989+1791
=1971.2×1989+1791
=1971×1989+0.2×1989+1791
=1971×1990+397.8
=3922687.8