Correct option is (b) 8%
Let the C.P. = Rs.100.
Then, the M.P. at 20% up = Rs(100 + 20) = Rs.120
The discount = 10% on the M.P.
∴ The S.P. = Rs.\(\left(120 - 120 \times \frac{10}{100}\right)\)
= Rs 108
So, the gain = S.P − C.P
= Rs(108 − 100)
= Rs. 8
∴ The gain percent = 8%.
(since the C.P. is Rs. 100).