ta có :
\(\overline{abcdeg}=\overline{ab}\cdot10000+\overline{cd}\cdot100+\overline{eg}\)
\(=\overline{ab}\cdot9999+\overline{cd}\cdot99+\left(\overline{ab}+\overline{cd}+\overline{eg}\right)\)
\(9999⋮11\Rightarrow\overline{ab}\cdot9999⋮11\)
\(99⋮11\Rightarrow\overline{cd}\cdot99⋮11\)
\(\overline{ab}+\overline{cd}+\overline{eg}⋮11\)
\(\Rightarrow\overline{abcdeg}⋮11\)