The cost price of 15 pens is equal to the selling price of 20 pens. The loss or profit percentage is:

Given,

The cost price of 15 pens is equal to the selling price of 20 pens

Let the cost price of 15 pens = $$a$$

$$=$$>  The cost price of 1 pen = $$\frac{a}{15}$$

The selling price of 20 pens = a

$$=$$>  The selling price of 1 pen = $$\frac{a}{20}$$

$$\therefore\ $$Loss% = $$\frac{\frac{x}{15}-\frac{x}{20}}{\frac{x}{15}}\times100=\frac{\frac{x}{60}}{\frac{x}{15}}\times100=\frac{15}{60}\times100=25\%$$

Hence, the correct answer is Option A