Correct Answer - Option 1 : 20% loss

Given:

The cost price of 20 books = Selling price of 25 books

Concept:

Gain: The amount gained by selling a product with more than its cost price.

Loss: The amount by which cost price is more than selling price.

Formula Used:

Loss = Cost price – Selling Price

Loss percentage = (Loss/Cost Price) × 100

Calculation:

Let the Selling price of one book be 10 x

So, the selling price of 25 books = 250x

Cost price of 20 books = 250x

⇒ Cost price of 1 book = 250x/20 = 12.5x

Loss = 12.5x - 10x = 2.5x

Loss % = (2.5x/12.5x) × 100 = 2500/125 = 20%

∴ The loss percent is 20%.