Gọi số cần tìm là ab
\(a+b+a.b=\overline{ab}\)
\(a.\left(b+1\right)+b=a.10+b\)
\(a\cdot\left(b+1\right)=a.10+b-b\)
\(a.\left(b+1\right)=a.10\)
\(b+1=a.10:a\)
\(b+1=10\)
\(\Rightarrow b=10-1\)
\(\Rightarrow b=9\)
\(\Rightarrow9+a+9.a=\overline{a9}\)
\(\Rightarrow10+9=a.10+9\)
\(\Rightarrow a.10=10+9-9\)
\(\Rightarrow a.10=10\)
\(\Rightarrow a=10:10\)
\(\Rightarrow a=1\)
\(\Rightarrow\overline{ab}=19\)
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