How many digit required to write numbers from 1 to 50 ?

$$\eqalign{ & {\text{No}}{\text{. of digits}} \cr & {\text{0 - 9 }} \to {\text{ 1}} \times {\text{9 = 9}} \cr & {\text{10 - 19 }} \to {\text{ 2}} \times {\text{10 = 20}} \cr & {\text{20 - 29 }} \to {\text{ 2}} \times {\text{10 = 20}} \cr & {\text{30 - 39 }} \to {\text{ 2}} \times {\text{10 = 20}} \cr & 40{\text{ - 49 }} \to {\text{ 2}} \times {\text{10 = 20}} \cr & 50\, \to \,2 \times {\text{1 = 2 = 91}} \cr} $$