A sum of money invested at compound interest amounts to Rs. 650 at the end of first year and Rs. 676 at the end of second year. The sum of money is = ?

Interest on 650 for one year = 676 - 650 = 26
$$\eqalign{ & 26 = \frac{{650 \times r \times 1}}{{100}} \cr & r = 4\% \cr & 650 = P\left[ {1 + \frac{4}{{100}}} \right] \cr & \Rightarrow 650 = P \times \frac{{26}}{{25}} \cr & \Rightarrow p = \frac{{650 \times 25}}{{26}} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\, = {\text{Rs}}{\text{.}}\,625 \cr} $$