7.49-[o.56=2.49] 21.43-2.17-7.83=8.57 都用简便计算

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7.49-[o.56=2.49] 21.43-2.17-7.83=8.57 都用简便计算

7.49-[o.56=2.49] 21.43-2.17-7.83=8.57 都用简便计算
7.49-[o.56=2.49] 21.43-2.17-7.83=8.57 都用简便计算

7.49-[o.56=2.49] 21.43-2.17-7.83=8.57 都用简便计算
7.49-(0.56+2.49)=7.49-0.56-2.49=7.49-2.49-0.56=5-0.56=4.44
21.43-2.17-7.83+8.57=21.43+8.57-2.17-7.83=(21.43+8.57)-(2.17+7.83)=30-10=20

21.43-2.17-7.83
=21.43-(2.17+7.83)
=21.43-10
=11.43
运用了减法的运算性质a-b-c=a-(b+c)