A trader bought an article and then sold. Had he bought at 10% less and sold at 10% more, he would have doubled his profit percentage.

The problem doesn't provide specific numbers for the cost price or selling price of the article, so let's solve it using variables.

Let's assume:

• The cost price of the article is C.
• The selling price of the article is S.
• The profit made by the trader is P = S - C.

According to the problem, if the trader had bought the article for 10% less and sold it for 10% more, he would have doubled his profit. So, we can write this as:

• The reduced cost price is 0.9C.
• The increased selling price is 1.1S.
• The new profit is P' = 1.1S - 0.9C.

According to the problem, P' is double the original profit P. So, we can write this as:

2P = P' 2(S - C) = 1.1S - 0.9C

Solving this equation will give us the relationship between the original cost price C and the selling price S.