A trader marks his goods at 30% above cost price and allows a discount of 10%.

Let the CP be Rs 100 .

Then, marked price $=$ Rs 130

Discount $=10 \%$ of MP

$=(10 \%$ of Rs. 130$)$

$=$ Rs. $\left(130 \times \frac{10}{100}\right)$

$=$ Rs. 13

Now, SP $=(\mathrm{MP})-($ discount $)$

$\quad=$ Rs. $(130-13)$

$\quad=$ Rs. 117

$\therefore$ Gain percentage $=(117-100) \%$

= 17%

$\therefore$ The gain percentage of the trader is $17 \%$.