A man bought 20 shares of Rs. 50 at 5 discount, the rate of dividend being 13 12 . The rate of interest obtained is:

Investment = Rs. [20 x (50 - 5)] = Rs. 900. 

Face value = Rs. (50 x 20) = Rs. 1000.

Dividend   =  $Rs.\frac{27}{2}*\frac{1000}{100}=Rs.135$ 

Interest obtained =  $\frac{135}{900}*100$ % = 15%