题目内容
3.计算:①5$\frac{6}{7}$-1$\frac{2}{5}$+4$\frac{1}{7}$-1.6;
②7$\frac{3}{4}$-1$\frac{1}{5}$-1$\frac{4}{5}$;
③8.5×9.9+85×0.01;
④4.2×75%-5$\frac{4}{5}$÷1$\frac{1}{3}$+$\frac{3}{4}$×2.4;
⑤12.5×64×0.25.
分析 ①根据加法交换律和结合律以及减法的性质进行简算;
②根据减法的性质进行简算;
③根据乘法分配律进行简算;
④根据乘法分配律进行简算;
⑤根据乘法交换律和结合律进行简算.
解答 解:①5$\frac{6}{7}$-1$\frac{2}{5}$+4$\frac{1}{7}$-1.6
=(5$\frac{6}{7}$+4$\frac{1}{7}$)-(1$\frac{2}{5}$+1.6)
=10-3
=7;
②7$\frac{3}{4}$-1$\frac{1}{5}$-1$\frac{4}{5}$
=7$\frac{3}{4}$-(1$\frac{1}{5}$+1$\frac{4}{5}$)
=7$\frac{3}{4}$-3
=4$\frac{3}{4}$;
③8.5×9.9+85×0.01
=8.5×9.9+8.5×0.1
=8.5×(9.9+0.1)
=8.5×10
=85;
④4.2×75%-5$\frac{4}{5}$÷1$\frac{1}{3}$+$\frac{3}{4}$×2.4
=4.2×0.75-5$\frac{4}{5}$×0.75+0.75×2.4
=(4.2-5$\frac{4}{5}$+2.4)×0.75
=0.8×0.75
=0.6;
⑤12.5×64×0.25
=12.5×(8×8)×0.25
=(12.5×8)×(8×0.25)
=100×2
=200.
点评 考查了运算定律与简便运算,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简便计算.
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