4. Please write the result of the expression $0 . \dot{1}+0.0 \dot{1}+0.00 \dot{1}$ as a simplified fraction.
4. $\frac{37}{300}$
4. 【Solution】Original expression $=\frac{1}{9}+\frac{1}{90}+\frac{1}{900}=\frac{100+10+1}{900}=\frac{111}{900}=\frac{37}{300}$.