题目内容

用简便方法计算
(1)678+(354+322)
(2)283+147+17+1653
(3)384-(37+184)
(4)2904-1327-173
(5)653-197
(6)125×17-125
(7)235×99
(8)(1300-520)÷13
(9)67×21+18×21+85×79
(10)222222×999999.
分析:(1)根据加法的交换律即可;
(2)根据加法的交换律和加法的结合律;
(3)和(4)根据连续减去两个数等于减去两个数的和;
(5)是用凑整百法,剩下的题目是利用乘法分配律.
解答:解:(1)678+354+322                                   
=678+322+354
=1000+354
=1354;
(2)283+147+17+1653
=283+17+(147+1653)
=300+1800
=2100;
(3)384-(37+184)
=384-(184+37)
=384-184-37
=200-37
=163;
(4)2904-1327-173
=2904-(1327+173)
=2904-1500
=1404;
(5)653-197
=653-200+3
=453+3
=456;
(6)125×17-125
=125×(17-1)
=125×16
=125×8×2
=1000×2
=2000;
(7)235×99
=235×(100-1)
=235×100-235×1
=23500-235
=23265;
(8)(1300-520)÷13
=1300÷13-520÷13
=100-40
=60;
(9)67×21+18×21+85×79
=21×(67+18)+85×79
=21×85+85×79
=85×(21+79)
=85×100
=8500;
(10)222222×999999
=222222×(1000000-1)
=222222×1000000-222222×1
=222222000000-222222
=222221777778.
点评:解答此题的关键是,根据题目特点,合理利用所学过的运算定律,让计算简便.
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