题目内容

用递等式计算(怎样简便就怎样计算).
0.25×5×1.6            
4.28+4.72×2.5
3.14×5.5+0.314×45     19.72×101-19.72
3.7×4.85+16.07         (0.718+0.718+0.718+0.718)×0.25.
分析:(1)把1.6拆成4×0.4,运用乘法交换律与结合律简算;
(2)把4.72看作1.18×4,运用乘法结合律计算第二项,然后再算加法;
(3)通过数字转化,运用乘法分配律简算;
(4)运用乘法分配律简算;
(5)先算乘法,再算加法;
(6)括号内写成0.718×4,然后运用乘法结合律简算.
解答:解:(1)0.25×5×1.6
=0.25×5×4×0.4
=(0.25×4)×(5×0.4)
=1×2
=2;

(2)4.28+4.72×2.5
=4.28+1.18×4×2.5
=4.28+1.18×(4×2.5)
=4.28+1.18×10
=4.28+11.8
=16.08;

(3)3.14×5.5+0.314×45    
=3.14×5.5+3.14×4.5   
=3.14×(5.5+4.5)
=3.14×10
=31.4;

(4)19.72×101-19.72
=19.72×(101-1)
=19.72×100
=1972;

(5)3.7×4.85+16.07        
=17.945+16.07
=34.015;

(6)(0.718+0.718+0.718+0.718)×0.25
=(0.718×4)×0.25
=0.718×(4×0.25)
=0.718×1
=0.718.
点评:.完成本题要注意分析式中数据,运用合适的简便方法.
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