题目内容

用递等式计算(能用简便方法计算的尽可能用简算)
(12)0.4×(3.2-0.8)÷0.15               (13)5.7+1.9×0.2÷7.6
(14)32.4×6.3+32.4×3.7                (15)18.2-10.6×(0.9-0.75)
(16)0.25×3.85×40                     (17)1.46×3.5+3.5×4.54.
分析:(12)先算括号内的,再算括号外的乘法和除法;
(13)先算乘除,再算加法;
(14)(17)运用乘法分配律简算;
(15)先算括号内的,再算括号外的乘法,最后算减法;
(16)运用乘法交换律与结合律简算.
解答:解:(12)0.4×(3.2-0.8)÷0.15,
=0.4×2.4÷0.15,
=0.96÷0.15,
=6.4;

(13)5.7+1.9×0.2÷7.6,
=5.7+0.38÷7.6,
=5.7+0.05,
=5.75;

(14)32.4×6.3+32.4×3.7,
=32.4×(6.3+3.7),
=32.4×10,
=324;

(15)18.2-10.6×(0.9-0.75),
=18.2-10.6×0.15,
=18.2-1.59,
=16.61;

(16)0.25×3.85×40,
=0.25×40×3.85,
=10×3.85,
=38.5;

(17)1.46×3.5+3.5×4.54,
=3.5×(1.46+4.54),
=3.5×6,
=21.
点评:此题考查了小数的四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算律简便计算.
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