The simple interest on a certain sum of money at the rate of 5% per annum for 8 years is Rs. 840. Rate of interest for which the same amount of interest can be received on the same sum after 5 years is = ?

$$\eqalign{ & {\bf{Case - I:}} \cr & {\text{SI}}\% = {\text{R}}\% \times {\text{t}} \cr & {\text{SI}}\% = {\text{5}}\% \times {\text{8}} \cr & = {\text{40}}\% \cr & {\bf{Case - II:}} \cr & {\text{SI}}\% = {\text{5}} \times {\text{r}}\% {\text{ }} \cr & {\text{According to the question}} \cr & \Rightarrow {\text{40}}\% = {\text{5}} \times {\text{r}}\% \cr & \Rightarrow {\text{r}}\% = {\text{8}}\% \cr} $$