We calculate the time in days
[tex]\bf{365 + 120 + 15 = 500 \text{ days}}[/tex]
We calculate the interest
52 500 € - 45 000 € = 7 500 €
We calculate the interest rate:
[tex]\large\displaystyle\text{$\begin{gathered}\sf \bf{\displaystyle t = \frac{7\:500}{45\:000 \cdot 500} = \frac{1}{3000}} \end{gathered}$}[/tex]
However, this is the daily rate of interest. To have the annual rate we must multiply by 365. Also, to have the rate as a percentage, we must multiply by 100:
[tex]\large\displaystyle\text{$\begin{gathered}\sf \bf{\displaystyle t = \frac{1}{3000} \cdot 365 \cdot 100 = 12.16\% } \end{gathered}$}[/tex]
Thus, the interest rate is 12.16% per year.
