If the simple interest on Rs. 1 for 1 month is 1 paisa, then the rate percent per annum will be = ?

$$\eqalign{ & {\text{t}} = {\text{1 month = }}\frac{1}{{12}}{\text{year}} \cr & {\text{SI = 1 paisa = Rs}}{\text{. }}\frac{1}{{100}} \cr & {\text{r}}\% = \frac{{{\text{SI}} \times {\text{100}}}}{{{\text{P}} \times {\text{T}}}} = \frac{{1 \times 100 \times 12}}{{100 \times 1 \times 1}} \cr & {\text{r}}\% = 12\% \cr} $$