(1.25-0.125)×8 =1.25×8-0.125×8 简便计算五年级=10-1 =9 (正用) (125+2.5)×0.8 =125×0.8+2.5×0.8 =1+1 =2 (正用) 3.72×3.5+6.28×3.5 =3.5×(3.5+6.28) =3.5×10 =35 (逆用) 二、把其中一个因数分成两个数的和或差，再按乘法分配律 0.8×100.1 =0.8×(100+0.1) =0.8×100+0.8×0.1 =80+0.08 =80.08 3.65×10.1 =3.65×(10+0.1) =3.65×10+3.65×0.1 =36.5+0.365 =36.865 0.32×403 =0.32×(400+3) =0.32×400+0.32×3 =128+0.96 =128.96 三、更改因数的小数点位置 6.66×3.3+0.666×67 =6.66×3.3+6.66×6.7 =6.66×(3.3+6.1) =6.66×10 =66.6 46×57+23×86 =46×57+46×43 =46×(57+43) =46×100 =4600 4.8×7.8+78×0.52 =4.8×7.8+7.8×5.2 =7.8×(4.8+5.2) =7.8×10 = 78 四、添加因数“1” 56.5×99+56.5 =56.5×99+56.5×1 =56.5×(99+1) =56.5×100 =5650 9.7×99+9.7 =9.7×99+9.7×1 =9.7×(99+1) =9.7×100 =970 4.2×99+4.2 =4.2×99+4.2×1 =4.2×(99+1) =4.2×100 =420 五、乘法交换律 0.25×8.5×4 =0.25×4×8.5 =1×8.5 =8.5 12.5×0.96×0.8 =12.5×0.8×0.96 =10×0.96 =9.6 0.5×0.34×0.6 =0.5×0.6×0.34 =0.3×0.34 =0.102 六、乘法结合律 4.36×12.5×8 =4.36×(12.5×8) =4.36×100 =436 0.95×0.25×4 =0.95×(0.25×4) =0.95×1 =0.95 0.75×50×0.4 =0.75×(50×0.4) =0.75×20 =15 七、拆数+乘法结合律 0.125×8.8 =0.125×8×1.1 =1×1.1 =1.1 0.25×0.28 =0.25×4×0.07 =1×0.07 =0.07 0.125×3.2×2.5 =(0.125×8)×(0.4×2.5) =1×1 =1
一、乘法分配律
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