题目内容
用简便方法计算 157-46-64 |
298+105 | 45×18 |
490÷35 | 175+36+25 | 490÷35÷2. |
分析:(1)连续减去46与64,等于减去46与64的和;
(2)298接近300,相差2,即加上300减去2即可;
(3)把18拆成2×9,再根据乘法交换律和结合律进行简算;
(4)把35拆成7×5,再根据除以7与5的积,等于连续除以7与5;
(5)根据加法交换律和结合律进行简算;
(6)连续除以35与2,等于除以35与2的乘积.
(2)298接近300,相差2,即加上300减去2即可;
(3)把18拆成2×9,再根据乘法交换律和结合律进行简算;
(4)把35拆成7×5,再根据除以7与5的积,等于连续除以7与5;
(5)根据加法交换律和结合律进行简算;
(6)连续除以35与2,等于除以35与2的乘积.
解答:解:
(1)157-46-64,
=157-(46+64),
=157-110,
=47;
(2)298+105,
=300+105-2,
=405-2,
=403;
(3)45×18,
=45×(2×9),
=(45×2)×9,
=90×9,
=810;
(4)490÷35,
=490÷(7×5),
=490÷7÷5,
=70÷5,
=14;
(5)175+36+25,
=(175+25)+36,
=200+36,
=236;
(6)490÷35÷2,
=490÷(35×2),
=490÷70,
=7.
(1)157-46-64,
=157-(46+64),
=157-110,
=47;
(2)298+105,
=300+105-2,
=405-2,
=403;
(3)45×18,
=45×(2×9),
=(45×2)×9,
=90×9,
=810;
(4)490÷35,
=490÷(7×5),
=490÷7÷5,
=70÷5,
=14;
(5)175+36+25,
=(175+25)+36,
=200+36,
=236;
(6)490÷35÷2,
=490÷(35×2),
=490÷70,
=7.
点评:用简便方法计算,使用合适的运算定律进行简算,不能直接使用运算定律的,要从拆分等方面入手进行简算.
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