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用简便方法计算:(1)0.3+0.6+1.2+2.4+4.8+9.6+19...

3个数算一个循环,等于0+0.3+0.6+...+9.6=0.3(1+2+...+32)=0.3*(1+32)*32/2

8+8+9=5,数圆圈就行 1+6+9,2个圆圈 3+4+6,1个圆圈 6+8+0,4个圆圈 8+8+9,5个圆圈

原式= (1/2)(2/3)(3/4)(4/5)(5/6)(6/7)(7/8)(8/9)/(0.1+0.9+0.2+0.8+0.3+0.7+0.4+0.6+0.5) 分子可以约分,约分后很简单,可得分子为1/9,分母组合后算出来是4.5,分子除以分母 原式=1/9/4.5=2/81

4.8 19.2

0.36+9.6÷0.32简便计算 0.36+9.6÷0.32 =0.36+9.6/3.2/10 =0.36+0.3 =0.66

1-2-3+4+5-6-7+8+9-10-11+12+...+2009-2010-2011+2012 =[1-2-3+4]+[5-6-7+8]+[9-10-11+12]+…+[2009-2010-2011+2012] =0+0+0+…+0=0

7.2x0.2+2.4x1.2 =2.4×3×0.2+2.4×1.2 =2.4×(0.6+1.2) =2.4×2-2.4×0.2 =4.8-0.48=4.32 2.22x9.9+6.66x6.7 =6.66×3.3+6.66×6.7 =6.66×(3.3+6.7) =66.6

答案是3,数圈。0有一个,1和3都没有,5没有6有一个,8有两个9有一个。

=(1-1/2)+(1-1/3)+...(1-1/10) =9-(1/2+1/3+...1/10) =9-[1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/9+1/10] =9-[(1/2+1/3+1/6)+(1/4+1/5+1/10)+1/7+1/8+1/9] =9-(1+11/20+1/8+1/7+1/9) =9-(1+27/40+1/9+1/7) =9-(1+283/360+1/7) =8-2341/2520

17×40=680, 100-63=37, 3.2+1.68=4.88, 2.8×0.4= 1.12 14-7.4=6.6, 1.92÷0.04=48, 0.32×500=160, 0.65+4.35= 5 10-5.4=4.6, 4÷20=0.2, 3.5×200=700, 1.5-0.06=1.44 0.75÷15=0.05, 0.4×0.8=0.32, 4×0.25=1, 0.36+1.54=2 1...

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