The marked price of an item is twice the cost price. For a gain of 15%, the discount should be:

Answer: Option D

Let CP = Rs. 100
MP = Rs. 200
Gain = 15%
SP = 100 + 15% of 100 = Rs. 115
Discount = 200 - 115 = 85
% Discount = $$\frac{85\times 100}{200}$$  = 42.5%