题目内容
18.用简便方法计算.69.5+18.7+1.3 9.37-4.56+3.63 1.25×2.5×3.2
4.5×0.8×1.25 0.45×3.8+6.2×0.45 9.9×6.3+0.63
7.8÷2.5÷4 3.9÷12.5÷0.8 10.1×8.5-0.85.
分析 (1)运用加法结合律进行简算;
(2)运用加法交换律进行简算;
(3)把3.2化成0.4×8,再运用乘法的交换律、结合律进行简算;
(4)运用乘法的结合律进行简算;
(5)运用乘法的分配律进行简算;
(6)运用乘法的分配律进行简算;
(7)运用除法的性质进行简算;
(8)运用除法的性质进行简算;
(9)运用乘法的分配律进行简算.
解答 解:(1)69.5+18.7+1.3
=69.5+(18.7+1.3)
=69.5+20
=89.5;
(2)9.37-4.56+3.63
=4.81+3.63
=8.44;
(3)1.25×2.5×3.2
=1.25×2.5×0.4×8
=(1.25×8)×(2.5×0.4)
=10×1
=10;
(4)4.5×0.8×1.25
=4.5×(0.8×1.25)
=4.5×1
=4.5;
(5)0.45×3.8+6.2×0.45
=0.45×(3.8+6.2)
=0.45×10
=4.5;
(6)9.9×6.3+0.63
=99×0.63+0.63
=(99+1)×0.63
=100×0.63
=63;
(7)7.8÷2.5÷4
=7.8÷(2.5×4)
=7.8÷10
=0.78;
(8)3.9÷12.5÷0.8
=3.9÷(12.5×0.8)
=3.9÷10
=0.39;
(9)10.1×8.5-0.85
=101×0.85-0.85
=(101-1)×0.85
=100×0.85
=85.
点评 本题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算定律进行简便计算.
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