The cost price of an article is ₹1,200. On buying four such articles, the customer gets one for free. If the selling price of each article is ₹1,800, then determine the net percentage profit earned by the shop keeper on selling four articles.

20%

Cost price of an article is Rs. 1200 

Selling price of an article is Rs. 1800

C.P. of 1 article = Rs.1200 

S.P. of 1 article = Rs.1800 

Also, on buying 4 articles 1 article is free for the customer

So, C.P. of 5 articles = 1200 × 5 = Rs. 6,000 

S.P. of 4 articles = 1800 × 4 = Rs. 7200 

Profit = 7200 - 6000 = Rs.1200 

Profit% = \(\frac{1200 × 100 }{6000}\)  = 20%