The marked price of a radio is 20% more than its cost price. If a discount of 10% is given on the marked price, the gain per cent is:

Answer: Option D

Let CP = 100
Then, MP = 100 + 20% of 100 = 120
Now, SP = 120 - 10% of 120 = 108
Gain = 108 - 100 = 8
%Gain = $$\frac{8\times 100}{100}$$  = 8%

Short-cut
100(CP) == 20%(up) ⇒ 120(MP) == 10%(disc.) ⇒ 108
% gain = 8%