The cost price of 18 articles is equal to the selling price of 15 articles.
Let the cost price of 1 article =₹1
Cost price of 18 articles =18×1
=₹18
Selling price of 15 articles =₹18
Selling price of 15 articles =₹18
Selling price of 1 article =1518
=₹1.2
Profit =Selling Price−Cost Price
=1.2−1
=₹0.2
Gain percentage =Cost PriceProfit×100
=10.2×100
=20%
Therefore, the gain percentage is 20%.