题目内容

脱式计算.
①2.7+3.1+2.9+3.2 ②0.44×8.3+8.3×0.56
③12.53-1.35×2-9.3 ④25×32×0.5.
分析:①根据加法交换律和结合律简算;
②运用乘法分配律简算;
③先算乘法,再根据减法的性质简算;
④先把32分解成4×8,再运用乘法结合律简算.
解答:解:①2.7+3.1+2.9+3.2,
=(2.7+3.2)+(3.1+2.9),
=5.9+6,
=14.9;

②0.44×8.3+8.3×0.56,
=(0.44+0.56)×8.3,
=1×8.3,
=8.3;

③12.53-1.35×2-9.3,
=12.53-2.7-9.3,
=12.53-(2.7+9.3),
=12.53-12,
=0.53;

④25×32×0.5,
=25×4×8×0.5,
=(25×4)×(8×0.5),
=100×4,
=400.
点评:此题是考查四则混合运算,要仔细观察算式的特点,灵活运用一些定律进行简便计算.
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