Correct Answer: 75%

Solution : Given: Selling 35 articles, the shopkeeper gains the selling price of 15 articles.
We know that, Selling price = Cost price + Profit
Let the selling price of an article be denoted SP and the cost price as CP.
⇒ 35SP = 35CP + 15SP
⇒ 20SP = 35CP
⇒ SP = $\frac{7}{4}$ CP
The gain is then given by:
Gain = SP – CP
= $\frac{7}{4}$CP – CP
= $\frac{3}{4}$ CP
Profit percentage = $\frac{\text{Selling price – Cost price}}{\text{Cost price}}×100=\frac{3}{4}\times100
= 75$%
Hence, the correct answer is 75%.