A man bought 20 shares of Rs. 50 at 5 discount, the rate of dividend being $$13\frac{1}{2}$$. The rate of interest obtained is:

$$\eqalign{ & {\text{Investment}} \cr & = Rs.\,\left[ {20 \times \left( {50 - 5} \right)} \right] \cr & = Rs.\,900. \cr & {\text{FaceValue}} \cr & = Rs.\,\left( {50 \times 20} \right) \cr & = Rs.\,1000. \cr & {\text{Dividend}} \cr & = Rs.\,\left( {\frac{{27}}{2} \times \frac{{1000}}{{100}}} \right) \cr & = Rs.\,135. \cr & {\text{Interest}}\,{\text{Obtained}} \cr & = \left( {\frac{{135}}{{900}} \times 100} \right)\% \cr & = 15\% \cr} $$