A shopkeeper by selling 21 items earns a profit equal to the selling price of 1 item. What is his profit percentage?

Let cost price of an item = $$Rs. x$$

Selling price of an item = $$Rs. y$$

=> Profit of 21 items = $$Rs. 21(y-x)$$

According to ques, => $$21(y - x) = y$$

=> $$21y - 21x = y$$

=> $$20y = 21x$$

=> $$\frac{x}{y} = \frac{20}{21}$$

Let Cost price, $$x = 20$$ and selling price, $$y = 21$$

$$\therefore$$ Profit % = $$\frac{y - x}{x} \times 100$$

= $$\frac{21 - 20}{20} \times 100$$

= $$\frac{100}{20} = 5\%$$

=> Ans - (D)