A tradesman marked his goods at 26% above its cost price and then allowed a discount of 13% . His gain (in %) is:

Correct option is B

Gain % = $$\frac{\text{(Selling Price - Cost Price)}}{\text{Cost Price}}$$​×100.
Solution:
Let cost price = 100.
Marked price = 100 + 26 = 126
Selling price = 126 − (126$$\times$$​0.13) =126 − 16.38= 109.62
Gain = 109.62 − 100 = 9.62
Gain % = $$\frac{9.62}{100} \times 100 = 9.62\%$$​​