题目内容

用递等式计算(能简算的要简算)
20.9+10.5÷(5-3.5)
3.5×0.7+5.5×0.7+0.7
10.64+7.65×2.4+11.76               6.2×9.9
9.83×(3.8-2.3)+1.5×6.17     ?     21÷0.25÷0.4.
分析:(1)先算乘除,再算加减,有括号的先算括号里面的;
(2)(4)(5)根据乘法分配律简便计算;
(3)先算乘法,再算加法;
(6)根据连除的简算方法计算即可.
解答:解:(1)20.9+10.5÷(5-3.5),
=20.9+10.5÷1.5,
=20.9+7,
=27.9;

(2)3.5×0.7+5.5×0.7+0.7,
=(3.5+5.5+1)×0.7,
=10×0.7,
=7;

(3)10.64+7.65×2.4+11.76,
=10.64+18.36+11.76
=29+11.76,
=40.76;

(4)6.2×9.9,
=6.2×(10-0.1),
=6.2×10-6.2×0.1,
=62-0.62,
=61.38;

(5)9.83×(3.8-2.3)+1.5×6.17,
=9.83×1.5+1.5×6.17,
=(9.83+6.17)×1.5,
=16×1.5,
=24;

(6)21÷0.25÷0.4,
=21÷(0.25×0.4),
=21÷0.1,
=210.
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律简便计算.
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