
0.12+0.23+0.34+0.45+0.56+0.67+0.78注意是循环小数,循环节在第二位
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0.12+0.23+0.34+0.45+0.56+0.67+0.78
=(0.1+0.2+0.3+0.4+0.5+0.6+0.7)+(0.02+0.03+0.04+0.05+0.06+0.07+0.08)
=(0.1+0.7)×7÷2+(0.02+0.08)×7×2
=0.8×7÷2+0.1×7÷2
=0.9×7÷2
=3.15
=(0.1+0.2+0.3+0.4+0.5+0.6+0.7)+(0.02+0.03+0.04+0.05+0.06+0.07+0.08)
=(0.1+0.7)×7÷2+(0.02+0.08)×7×2
=0.8×7÷2+0.1×7÷2
=0.9×7÷2
=3.15
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