题目内容

18.
递等式计算,能简便的用简便方法计算
0.25×1.7×0.4     

4.5×10.2    

1.28×7.5+2.5×1.28    
2.5×64×12.520.06×8.5+200.6×0.15     2.5×0.32+0.32×7.5       
8.8+3.2÷2.51.25×2.5×4×0.8    8.4×0.3÷0.12     
25×(0.4+0.8)3.5×99+3.5101×27-27     
1.25×0.8+1.2×1.25     1.25×88       32×0.125×0.25
6.4×0.21-0.86    6.8×0.75÷0.5     2.05÷0.82+33.6    
1.53+23.4÷7.2.

分析 (1)(5)(8)运用乘法交换律和结合律简算;
(2)把10.2看作10+0.2,运用乘法分配律简算;
(3)(6)(10)(11)(12)(13)(14)运用乘法分配律简算;
(4)把64看作4×2×8,运用乘法分配律简算;
(7)先算除法,再算加法;
(9)调整运算顺序,使计算简便;
(15)把32看作4×8,运用乘法交换律和结合律简算;
(16)先算乘法,再算减法;
(17)先算除法,再算乘法;
(18)(19)先算除法,再算加法.

解答 解:(1)0.25×1.7×0.4 
=(0.25×0.4)×1.7
=0.1×1.7
=0.17

(2)4.5×10.2
=4.5×(10+0.2)
=4.5×10+4.5×0.2
=45+0.9
=45.9

(3)1.28×7.5+2.5×1.28    
=1.28×(7.5+2.5)
=1.28×10
=12.8

(4)2.5×64×12.5
=(2.5×4)×2×(8×12.5)
=10×2×100
=2000

(5)20.06×8.5+200.6×0.15
=20.06×(8.5+1.5)
=20.06×10
=200.6

(6)2.5×0.32+0.32×7.5
=0.32×(7.5+2.5)
=0.32×10
=3.2

(7)8.8+3.2÷2.5
=8.8+1.28
=10.08

(8)1.25×2.5×4×0.8 
=(1.25×0.8)×(2.5×4)
=1×10
=10

(9)8.4×0.3÷0.12     
=(8.4÷0.12)×0.3
=40×0.3
=12

(10)25×(0.4+0.8)
=25×0.4+0.8×25
=10+20
=30

(11)3.5×99+3.5
=3.5×(99+1)
=3.5×100
=350

(12)101×27-27     
=(101-1)×27
=100×27
=2700

(13)1.25×0.8+1.2×1.25     
=1.25×(0.8+1.2)
=1.25×2
=2.5
   
(14)1.25×88       
=1.25×(80+8)
=1.25×80+1.25×8
=100+10
=110

(15)32×0.125×0.25
=4×8×0.125×0.25
=(4×0.25)×(8×0.125)
=1×1
=1

(16)6.4×0.21-0.86    
=1.344-0.86
=0.484

(17)6.8×0.75÷0.5 
=6.8×(0.75÷0.5 )
=6.8×1.5
=10.2

(18)2.05÷0.82+33.6
=2.05÷0.82+33.6
=2.5+33.6
=36.1

(19)1.53+23.4÷7.2
=1.53+3.25
=4.78

点评 此题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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