用简便方法计算:
78.6+1.9;
64.3-19.3-20.7;
72×125;
0.98×360+0.02.
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解:(1)78.6+1.9,
=78.6+(2-0.1),
=78.6+2-0.1
=80.6-0.1,
=80.5;
(2)64.3-19.3-20.7,
=64.3-(19.3+20.7),
=64.3-40,
=24.3;
(3)72×125,
=9×8×125,
=9×(8×125),
=9×1000,
=9000;
(4)0.98×360+0.02,
=(1-0.02)×360+0.02,
=360-0.02×360+0.02,
=360-7.2+0.02,
=352.82.
解析分析:(1)把1.9看作(2-0.1),计算简便;(2)运用减法的性质简算;(3)把72看作9×8,运用乘法结合律简算;(4)把0.98看作(1-0.02),运用乘法分配律简算.
点评:完成本题要注意分析式中数据,运用合适的简便方法计算.