If an article is sold at a 200% profit, this means that the selling price is 300% of the cost price. The ratio of the cost price to the selling price can be expressed as a fraction, with the cost price as the numerator and the selling price as the denominator.
Since the selling price is 300% of the cost price, the fraction representing the ratio of the cost price to the selling price is 1/3.
So the ratio of the cost price to the selling price is 1/3.