If a student of the mathematics department sells all his books for Tk. 7,500, he loses 25%. To gain 10%, at what price should he sell the books?

Question: If a student of the mathematics department sells all his books for Tk. 7,500, he loses 25%. To gain 10%, at what price should he sell the books?

Solution:
Let,
The cost price of the books x.
Selling price = x - 25% of x
⇒ 7500 = x - (25x/100)
⇒ 7500 = 75x/100
⇒ 75x = 750000
∴ x = 10000

To gain 10% = 10000 + 10% of 10000
= 10000 + 1000
= Tk. 11000

To gain 10%, he should sell the books for Tk. 11000.