If 5% more is gained by selling an article for Rs. 350 than by selling it for Rs. 340, the cost of the article is:________?

Let Cost price of the article be Rs.x

When Selling price is Rs.340 then,
Gain% = (340-x)/x * 100

When Selling price is Rs. 350 then,
Gain% = (350-x)/x * 100

Hence,
Additional % gain= (350-x)/x * 100 – (340-x)/x * 100
Additional % gain= 5=[350−x−340+x] * 100/x [It is given that gain% = 5%]

5x=1000
x=Rs.200

Cost price of article is Rs.200