The cost price of 72 books is equal to the selling price of 60 books. What is the gain percent ? 

Given:

The cost price of 72 books is equal to the selling price of 60 books.

Formula used:

Gain Percent = ^Gain/_{Cost Price} × 100

Gain = Selling Price - Cost Price

Calculation:

Let the cost price of 1 book be ₹C.

Cost Price of 72 books = 72C

Selling Price of 60 books = 72C

Selling Price of 1 book = ^72C/₆₀ = 1.2C

Gain = Selling Price - Cost Price

⇒ Gain = 1.2C - C = 0.2C

Gain Percent = ^0.2C/_C × 100

⇒ Gain Percent = 0.2 × 100 = 20%

∴ The correct answer is option (4).