题目内容
8.用递等式计算(能简便计算就简便计算,并写出主要计算过程)2.5×9.6×1.25 | (6.9+6.9×3)×2.5 |
14.66-7.38+2.34-2.62 | (3.8-7.7÷2.5)×(1-0.45) |
0.74÷0.8÷0.37 | 3.2×5.8+69×0.58-0.58 |
分析 (1)根据乘法交换律和结合律进行简算;
(2)根据乘法分配律和乘法结合律进行简算;
(3)根据加法交换律和结合律以及减法的性质进行简算;
(4)先算除法,再算减法,最后算乘法;
(5)根据除法的性质进行简算;
(6)根据乘法分配律进行简算.
解答 解:(1)2.5×9.6×1.25
=2.5×(4×8×0.3)×1.25
=(2.5×4)×(8×1.25)×0.3
=10×10×0.3
=100×0.3
=30;
(2)(6.9+6.9×3)×2.5
=6.9×(1+3)×2.5
=6.9×4×2.5
=6.9×(4×2.5)
=6.9×10
=69;
(3)14.66-7.38+2.34-2.62
=(14.66+2.34)-(7.38+2.62)
=17-10
=7;
(4)(3.8-7.7÷2.5)×(1-0.45)
=(3.8-3.08)×(1-0.45)
=0.72×0.55
=0.396;
(5)0.74÷0.8÷0.37
=0.74÷0.37÷0.8
=2÷0.8
=2.5;
(6)3.2×5.8+69×0.58-0.58
=32×0.58+69×0.58-0.58
=(32+69-1)×0.58
=100×0.58
=58.
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定律简便计算.
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