A shopkeeper increases the selling price of an article by 15%. After increasing the selling price, he noticed that the profit percentage changed from 5% to 15%. The percentage increase in the cost price is:

5%

Let the Selling price firstly = 100

Then the selling price secondly = 115

The Cost price firstly = 100 × \(\frac{100}{95}\) = \(\frac{2000}{19}\)

The Cost price Secondly = 100

change in both the cp = \(\frac{2000}{19}\) - 100 = \(\frac{100}{19}\)

Percentage change =  \(\frac{100}{19}\) × 100 × \(\frac{19}{2000}\) = 5%