$12\frac{1}{2}\%$

$13\frac{1}{2}\%$

15%

$16\frac{2}{3}\%$

C. 15%

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

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

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

Interest obtained =$\left(\frac{135}{900}x100\right)\%=15\%$