不好意思,理解错了,用拆分法就行,0.111...=1/9,0.200200200...=1/5+1/5000+...=1/5*(1-(1/1000)^n)/(1-1/1000)=200/999,所以0.311311...=1/9+200/999=311/999,其实你原来是对的