题目内容
脱式计算,注意使用简便方法
①12×
÷
②(2+
)×18
③
×
+
④77×
+23×0.8
⑤
÷[(
)×
].
解:①12×
÷
=12×
×
,
=6;
②(2+
)×18
=2×18+
×18,
=36+4,
=40;
③
×
+
=
+
,
=
;
④77×
+23×0.8
=77×0.8+23×0.8,
=(77+23)×0.8,
=100×0.8,
=80;
⑤
÷[(
)×
]
=
÷[
×
],
=
×6,
=
.
分析:①可根据乘法交换律计算;
②④可根据乘法分配律计算;
③⑤根据四则混合运算的运算顺序计算即可:先算乘除,再算加减,有括号的要先算括号里面的.
点评:完成有关于分数四则混合运算时要细心,注意通分约分.


=12×


=6;
②(2+

=2×18+

=36+4,
=40;
③



=


=

④77×

=77×0.8+23×0.8,
=(77+23)×0.8,
=100×0.8,
=80;
⑤



=



=

=

分析:①可根据乘法交换律计算;
②④可根据乘法分配律计算;
③⑤根据四则混合运算的运算顺序计算即可:先算乘除,再算加减,有括号的要先算括号里面的.
点评:完成有关于分数四则混合运算时要细心,注意通分约分.

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