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0.1+0.2+0.3+0.4+……+2.5的简便方法

类似高斯故事里的计算,让我们先观察一下算式,发现可以分组求和,首先为了方便计算可以先提取十分之一,然后再1+25 2+24 3+23 这样分成若干组和为26的算式,最后计算组数发现有12组,再加上落单的13,整理就得到最终结果32.5了,这是等差数列的...

0.1+0.2+0.3+0.4+…+2.5 =(0.1+2.5)x25÷2 =2.6x25÷2 =1.3x25 =32.5

2,5X4X2.3 0·29X100+0.29*2 2.5*(1.2+0.8 ) 1.25*8*(0.4*2.5) 1/8*72 0.25*(39+1)

0.1+0.3+0.5+0.7+……+0.99 =(0.1+0.3+...+0.9)+(0.11+0.13+...+0.99) =(0.1+0.9)*5/2+(0.11+0.99)*45/2 =2.5+22.5*1.1 =2.5+24.75 =27.25.

1.2×5.2一2.5÷0.3 =1.2x(5+0.2)-(2.4+0.1)÷0.3 =1.2x5+1.2x0.2-2.4÷0.3-0.1÷0.3 =0.3x4x5+0.24-8-1/3 =0.3x20+0.24-8-1/3 =6+0.24-8-1/3 =-2+0.24-1/3 ≈-2+0.24-0.34 =-2-0.1 =-2.1

(4+0.4)x2.5 =4×2.5+0.4×2.5 =10+1 =11

1.2x2.5+0.8x2.5 =(1.2+0.8)x2.5 =2x2.5 =5

=(1.2+0.8)*2.5 =2*2.5 =5

(1)12.5×0.4×2.5×8=12.5×8×0.4×2.5=(12.5×8)×(0.4×2.5)=100×1=100(2)9.5×101=9.5×(100+1)=9.5×100+9.5×1=950+9.5=959.5(3)4.2×7.8+2.2×4.2=4.2×(7.8+2.2)=4.2×10=42 (4)0.8×72.4×12.5=0.8×12.5×72.4=10×72.4=724

0.2÷2.5×(4.2-1.075) =0.2×0.4×3.125 =0.08×3.125 =0.08×3+0.08×0.125 =0.24+0.01 =0.25

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